Thank you to
@Execute/Dumbo and
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@Durin
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Rakshasas
Rakshasas are a fully psychic race of sapient bipeds native to Avernus that look like a combination of tiger and lynx, though furless. Their most defining characteristic is their high level of battle power for their size, even compared to other Avernite Peoples. They are a warrior race through and through.
***
Biology
Rakshasas are omnivores that lean towards carnivorous preferences. They'll snack on anything nearby, but prefer to go after energy-rich meat to maintain their high-energy lifestyles. Rakshasas like to spend most of the average day training their bodies and fighting abilities to perpetually increase their effectiveness as warriors.
Rakshasas are enabled in their perpetual quest for power by their unique physiques - their central nervous systems act as anchor points that make their bodies and souls more linked together than other species, and this provides a number of benefits.
Training the body increases the power of the rakshasa's soul, which in turn increases the potential strength the rakshasa's body can reach. Because of this, a rakshasa's body can become more powerful than physically possible, and in theory allows for unlimited physical and spiritual growth, like an ork. The body also gets small resistance to mundane damage and diseases and faster healing when the soul is healthy.
The most dramatic advantage the rakshasas' unique condition grants them is easy access to a daemonology technique known as Aurai. Aurai summons the user's soul into reality and fuses it with their body, giving them all the relative supernatural durability, physical capability, and psychic strength of an unbound daemonhost. While any daemonologist can theoretically learn the technique, it's almost exclusively the domain of masters of the discipline. For the rakshasas, however, Aurai is easy enough that manifesting the power is simply a rite of passage into adulthood. However, since this ease relies on the rakshasas' central nervous system, electrical attacks and certain psychic poisons are good ways of shutting down the power when rakshasas use it. In the case of rakshasas, using the power makes them more aggressive as their brains have evolved to interpret the use of the technique as a sign of battle. Aurai does have a pair of notable weaknesses, however. Any damage taken during the use of the power is marked upon the surface of the soul, which retards the physical body's healing until the soul has finished mending itself. Additionally, the power makes the user vulnerable to powers that target the soul itself, such as the Purge Soul daemonology power.
Another physical feature the rakshasas have is a small but dense cache of a special kind of psychically impregnated fat separate from the body's regular fat reserves. This cache is extremely energy rich and takes a very long time to build up without constant feasts. The body only accesses this cache when hitting its regular stamina limit in combat, in essence giving rakshasas a substantial second wind in exhausting battles. Additionally, the fat's psychically potent nature means that the rakshasa's psychic powers are boosted while the body is burning this fuel, potentially making the rakshasa even deadlier than when the battle started.
***
Ways of Life
Rakshasas are adaptable enough that they can live different ways of life, not limited to any one particular lifeway.
Many rakshasas live as nomadic pastoralists who travel on and with their herds of fauna, sustaining themselves on the meat and secretions of their herds as they move from grazing ground to grazing ground. Getting food from domesticated beasts is much easier and safer than hunting for it and is quite beneficial to the rakshasas, as the reduced energy loss, time cost, and wound potential means they can train their martial skills more. The introduction of grox via distant traders has greatly improved the lot of these rakshasas, as it has all Avernite livestock owners who've adopted them. They're battle-capable enough to survive Avernus but domesticable to a degree that the sapient natives need not fear being destroyed by them. When you add their extremely high nutritional value, they make ideal livestock for the planet's denizens.
Rakshasas also exist in sedentary civilisations in small, independent kingdoms, oftentimes ruling over just a single small city and nearby villages as typical city states. These kingdoms are very hierarchical, with a relatively small group of elites holding the power while the rest work to provide food and other resources. While the latter group does outnumber the former, they spend their lives not training or fighting, but working, while that's what the elites mainly do. This gives the elites an overwhelming qualitative edge that they can use to suppress all revolts against their rule. Their subjects are typically unable to leave both due to restrictions placed upon them by the rulers and by how their lack of training makes them reliant on their overlords for protection against Avernus. These kingdoms are major slave owners and raiders. All in all, these kingdoms are almost the same as early human kingdoms.
The third and final major way that rakshasas live their lives is as part of mercenary companies, hiring themselves out to civilisations for food and riches in exchange for military assistance. While several such companies are of an immoral nature (turning brigand when not under contract, founding kingdoms, etc.), honourable and even noble ones can be found, though in the case of the former they typically charge a higher price for their services.
Of course, these lifeways aren't the only way that rakshasas can live, just the most common. Hunter-gatherer groups of rakshasas still exist in more isolated areas of Avernus, for example. One of these minor ways of life is, however, particularly notable, even despite the low number of rakshasas who live them: monasticism.
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Faith and Monastic Orders
While rakshasas are a very geographically diverse race, most share a common core of faith. They believe that every species has an idealised form, and that the closer one comes to reaching that idealised form, the higher their cosmic standing both in reality and the Warp is. The rakshasas believe that the idealised form of not just them, but all mortals, is not gods, but higher order material beings.
The reasoning behind this idea is something of a split amongst rakshasas. Some believe that it's because of the separation between warp and reality. As warp entities and mortal beings are two intrinsically separate things, their ideal forms would be intrinsically separate, with one being a higher warp entity and the other being a higher mortal being. Others argue that it's because warp entities are intrinsically lesser than mortal beings, that they're half-mortals - soulful, but lifeless. Their belief that it's easier for these higher beings to become gods than the reverse is proof of this, as it's easier to descend than ascend, as common sense dictates.
In the case of the rakshasas, they believe that as they're a warrior race, the path for a rakshasa to reach their pinnacle is to become the ultimate warrior. The monks and nuns of the rakshasas' monastic orders have dedicated their lives to climbing this ladder, becoming, in their eyes, higher beings as they do so. In this goal, they take to living ascetic lives, giving up worldly distractions to better focus their efforts on their eternal quest for ascension.
Each of the rakshasas' monastic orders have their own monastery where they can further themselves in seclusion from the rest of the world. Despite their seclusion, however, the monastic orders do keep in touch with each other and meet every so often to discuss matters relating to the orders as a whole, hold a small tournament, and vote on things when necessary. Each leader of an order - known as the grandmaster of their order - gets a number of votes determined by how well their chosen combatant of their order does in the tournament.
Of course, the warrior-monastics of the rakshasas do have basic needs that need to be fulfilled - gathering food, maintaining their dojo-monasteries, and other things of that nature. These activities would take away time and energy the monastics could instead use to become stronger, and so by necessity have come to rely on outside aid to fund themselves. How exactly they receive the necessary assistance varies from place to place. Sometimes, communities form around the monasteries and donate assistance, and in return the monastics will defend the communities when they themselves cannot. Others will offer training in exchange for support, go mercenary for brief periods of time, or take slaves.
The various monastic orders of the rakshasas have naturally developed very different cultures from one another, sometimes to a near antithetical level. Only centuries of tradition keeps the faith united, with very strict rules governing feuds, duels, and even small scale wars preventing things from spiralling out of control.
***
Martial and Psychic Traditions
Physical combat and the use of psychic powers are, for most of the rakshasas, one and the same. Through martial arts they learn to not only hone their bodies, but focus their minds, and over the generations the warriors of the rakshasa race have learned to exploit the connection between body and soul to its fullest potential. By the time they're adults, they will have learned how to harden their bones and skin against damage, push psychic energy through their muscles for potent bursts of strength and speed, and heal injuries more quickly during times of rest and recovery.
Greater however are the benefits of their training on their central nervous system, that which grounds their souls to their bodies. There the total conscious power of a sapient mind is fully realised, particularly given that the brain, the seat of consciousness, is part of the central nervous system. Their reflexes and reaction speeds go through the roof, their minds gain shields of electric wire, and their ability to predict the immediate future edges into true precognition.
The greatest weakness of the rakshasas is their difficulty in manifesting most traditional psychic powers. Their bodies ground their powers, making it easy for them to channel it in ways that enhance their natural capabilities, but very difficult to do anything besides that. The exception to this are those who train in the monastic orders. There, through secret methods kept extremely tightly held and never taught to those outside the orders, the monastics learn to open their chakra pathways and switch their bodies from being grounding to being channels through which their power can flow, to awesome effect. The powers they learn to manifest complement and accentuate their fighting style; it's quite rare for any to learn powers that don't work in conjunction with a martial arts-centric style of combat.
***
Upheaval
Recent times have been marked by great upheaval within the rakshasa race.
To begin with, the introduction of grox to the nomad populations has greatly increased their relevance. There are more nomads, the nomads are more individually powerful, and they can now live in certain parts of the world much more easily than before. This has let to numerous situations both good and bad between the nomads and those they newly meet, the civilisations of the rakshasas and of other races.
Amidst the kingdoms, a new Maharaja, a Great King, seems to be rising. On occasion, a warrior of exceptional might will rise above all the other rajas, kings, and all would bend the knee after their first few conquests have proven their might, but this one is different. Exiled as a child for his weakness, he went on to not only gain great strength, but also an education amidst another civilisation. Now, after returning to his home, he has not only started conquering but has also begun enacting sweeping administrative reforms that threaten the entrenched positions of the rulers and elites even in peace. Widespread, continued resistance against his conquests from those kingdoms not yet under his rule have sprung up as a result, and it's unknown which of the two sides will ultimately emerge victorious.
Recently, one of the monastic orders has been excommunicated and branded traitors. This is the first time this kind of verdict has ever been given for an entire order. Seduced with promises of power and virtual immortality, the renegade order joined the Empire where they have been sharing the monastics' secrets. This has, in turn, sparked great conflict between the orders and the Empire. Now with their monopoly broken and the inherent challenge to their authority that are the renegades, the future of the monastic orders is greatly in question.
As for the renegades themselves, the promises made to them were fulfilled in their entirety. A few rakshasas lived in the Empire, and in their Aurai power the Empire saw similarities to the daemonically possessed. Daemonhost preparation rituals were something high level cults could get access to, and so with more resources, talent, and freedom to operate, the Empire sought to create a non-Chaos, soul-focused analogue that kept the mind intact. In this goal they succeeded. In fact, the process was markedly cheaper and simpler than daemonhost creation, as one's own soul had natural synchronicity with the body, and less fortification was required as souls weren't inherently corrosive to mortal life as daemons were. The only significant requirement was for the subject to maintain the power throughout the process. Once complete, the subject would remain in Aurai permanently. As a bonus, since the subject no longer needed to focus and channel energy to maintain the power, they were stronger now they were before when they used it. Also, once these bodies became infused with an unaging soul, their own aging slowed to such a crawl that it became all but inevitable that they'd die before senescence started slowing them. (Assuming they were already young, of course.)
There is one notable downside to the procedure, though. The souls of mortals exist just as much in the Warp as in reality, but when one uses Aurai, the souls are entirely in the Materium. Bereft of the presence of the Immaterium, the soul begins to cool and slow, collapsing without the dynamic energy of the Aether to keep it warm. The ordinary Aurai technique is too short-lived for this to ever matter, but for permanent Aurai, this will eventually cause a deep chilling pain and sanity loss as the mind, body, and soul slowly rot away to nothing. To counter this is not a complex affair, however, as it's analogous to how warm-blooded creatures keep warm. They can consume the life force of living creatures to invigorate themselves, use psychic powers or do passionate things as an analogue to exercise, or reside in a place loaded with the ambient energy of the Warp. (Such as Avernus.) This is a price the renegade monastics willingly pay, as for them, the power and longevity they gain is very much worth the price of what they see as essentially eating, breathing, and fighting.
Perhaps most momentously, with the new "soulhosts", a new breed of rakshasas has been born. Rakshasas can handle high levels of psy energy flowing through their bodies, and gestating rakshasas get additional protection from a drip feed of their mother's spinal fluid. As a result, when a mother has Aurai active all throughout a pregnancy, the success chance of what would've otherwise been a successful pregnancy were it not for continuous Aurai is 1% for a rakshasa, as opposed to 0% for other races. Rakshasas exposed to such an abundance of refined psychic energy during their gestation are different from ordinary rakshasas, mutated. They're much more powerful than other rakshasas their age, though most of this additional power lays dormant. In Aurai, this power bursts forth and overloads their brains' ability to handle it. They lose themselves entirely to the battle aggression, the only parts of their brains still working at full capacity being the parts that know how to fight and learn how to fight. In fact, these areas get instinctively supercharged, so these rakshasas are not only stronger in Aurai than normal rakshasas, but more skilled.