As mentioned before, Stephan essentially said 'please, come onto my shores, and try to get down through the forest' and then utilized Eonir forestry experience and Nordland forestry experience to 24/7 harras, skirmish, and ambush the Druchii as they tried to penetrate deeper into Nordland after finding out that somehow every single coastal settlement had been evacuated beforehand. There was nothing to plunder, only buildings to raze, but those can be rebuilt, so the Druchii kept trying to march deeper, looking for all the humans to kill. They've raided Nordland before, after all, they know what they're doing.
But then this raiding band disappears. Then this one is found shot dead full of arrows. Then another band of riders is shot apart. A flock of birds flew over an encampment that was in the process of being built and had bombs dropped all over it. Assassins, sneering, disappear into the trees proclaiming that they will ensure the enemy cannot harass them like that anymore. They do not return. A sorceress is about to kill a group of Nordlanders and their pathetic little human magisters, and then finds herself crushed under the weight of multiple Eonir mages who are in fact older than her and willing to use both High and Dark Magic. Stronger force concentrations are sent out, proper armed blocks, guarded by powerful warbeasts, with harpies scouting the skies alongside Dark Flyers on their Dark Pegasi.
They find themselves ambushed by Nordland artillery parks, spotted for by Eonir scouts and shrouded magically by Eonir communing with the wood and casting their own spells, blown apart while treemen and tree-kin come stomping out of the trees, while cavalry strikes them from behind.
Stragglers are allowed to flee.
Into the forest.
The Druchii, enraged, begin setting fire to the forests around them to deny the enemy cover. This happens to massively enrage the wood spirits, who begin marching out in greater strength. While the Druchii are distracted with them, Eonir and Nordland troops continually back them up with ranged fire, riding skirmishers close and firing and retreating, and so on. The Druchii are not allowed to rest, not allowed to recover, as their enemies continually cycle their troops, literally attacking them day in and day out, and when the Druchii try to chase back after them, the literal trees move and they disappear into them. When they don't, and the Druchii think they have them, coming down the roads, the forested sides of those roads end up to contain more troops, creating constant crossfires of arrow, crossbow, bullet, and cannon. After the harpies and Dark Flyers are terribly reduced in number, Eonir war hawk riders wielding fire arrows empowered with Aqshy from their mages start appearing at night to begin attacking the Druchii ships, including the bigger ones. If the Druchii try to hunt the enemy down with superior numbers, the camps and supplies they leave behind are attacked. Nordland and Eonir will rather shoot a single arrow and scratch a Druchii and retreat without taking any casualties themselves than try to get into protracted fights. The Shackled are wiped out early, utilized as meat shields as the Druchii try to get to grips with the enemy, or actually get them with their own ranged weapons.
The raiders are raided, endlessly.
The war beasts are fully unleashed, and the war beasts are felled by concentrated artillery fire while other troops hold off the Druchii themselves.
Yhanna Sunweaver, High Spellweaver of the High Realm of Laurelorn, confronts the Supreme Sorceress Xenatha Nightscreamer, and outright defeats her in a magical duel in one of a handful of actual protracted fights involving four digits of troops on the battlefield.
Stephan von Kessel openly reveals and identifies himself on the fielding, causing Fleetmaster Vorthal Nightfiend to order a great effort to capture him to try and break the spirit of the enemy, only to be caught in an ambush, and despite cutting his way free to escape back to the shoreline, ends up dead along the way as the collective knights of Nordland charge after him and his retreating force, cutting him down amidst the scrum, no one knows exactly who killed him, due to the state of his remains.
Due to the raiders standard tactics being dispersal and plundering in individual bands, it takes some time for them to reflexively reform back to a concentrated armed force as they begin altering gear and tactics to prepare for a much harder fight than they initially anticipated, especially after taking so many major casualties. Individual raiding bands are all called back, and the Druchii discipline begins reasserting itself. No longer can the enemy harass them from the skies or the distance, as they start building static defenses, start hauling Bolt Throwers off the ships to boost their defenses.
The forests get closer, and bombardment begins at a distance.
A day later, the whole of Nordland's armed forces are present previously, not including those elsewhere in the province, charges the beachheads at Norden, which is where all the ships have come after losing dispersed ships at other settlements. At the same time, the Eonir arrive with the rest of the Fleet of Nordland which has been hidden in Laurelorn territory, shoved up the rivers to be missed at the shoreline previously. During the battle, Stephan von Kessel and Crow Feeder are credited with killing the remaining Fleetmaster who was attempting to rally the Druchii, and then slew the Sea Dragon of the Death Fortress that Fleetmaster Nevis Duskreaver was commanding from by leaping from the castle's walls and onto its head - or, more accurately, plunging himself through the dragon's eye sword-first. Naraiel Dawnstone fights off a quintet of Khainite assassins at the same time, as the assault krakens are goaded halfway onto the shore. One is brought down through concentrated artillery fire, the other has forest dragons shove multiple blasts of sophorific breath into its open beak, paralyzing and slowing it long enough for Naraiel's other troops to manuever around it and kill several more Druchii. Meanwhile, the Silver Manticore charges for the beast and kills the assault kraken with his Tooth of Tlang.
The Druchii do not begin attempting surrender until the vast majority of them are dead, for various reasons, ranging from refusing to do to humans to not realizing how many of them were dead because of how fast the battle was. Around only a third of Druchii losses occurred in the fighting up until this point, with 2/3 killed in a single crushing battle of Nordland+Eonir hammer and anvil. The forest dragons do not release burning or acidic breath, but it is quite effective nonetheless at silencing Druchii and warbeasts without overly harming the ships. Some of the helldrakes and sea dragons escape out into the Sea of Claws, but many others are killed by brave Eonir and Nordlanders.
A massive amount of Druchii ships are captured.
Stephan says 'mount up.'
Then they all turn around on their ships and begin sailing east, leaving behind a token amount of troops to make sure that the forest spirits don't get a little to blood drunk with the amount of corpses and what not left behind. Bloodglade has the two assault kraken bodies, even.
Nariael says 'we can go faster, so we will.'
And so the Eonir Spellweavers and the Imperial Wizards collectively reach up and grab the Winds and say 'We're going to Ostland NOW.'
And then they showed up and decided to ram the collective Fleet of Nordland which took a bare handful of losses in the previous fighting and all the Druchii ships they captured into the collective ass of the Black Ark known as the Eternal Fortress of Torture, beaching and invading them en masse, while the majority of the Ark's fighting capacity was elsewhere i.e. at the walls of Salkalten.