don't make her drink her pain away, if that's what she's doing.
It might be that she is drinking pain, to bolster her stereotyped behavior and
resolve. Memories of long ago, and Guilt are in that flask. It has spoiled with age. Imagining it is interesting that way?
Attempting to get ahead of the missing evidence, and understand the character better using supposition.
We have a few excellent data points, so I feel it is not futile. We will get more.
I know this goes beyond the facts, the point is attempting the full model sooner, rather than later. Invalidation is part of science. So is forming a hypothesis, so here it goes.
Rionna probably lives an inflexible life she doesn't want. She is trapped.
Rionna is a regret driven avenger. Vengeance nor restoration will not be possible in her view. Friends and cooperation are just fiction to her. She burned out a long time ago, yet she keeps a reminder of every wrong thing she has done. Her Shades serve as trophies of her crimes. Pain is her daily companion. No one else can judge her - Because she has already been judged, by someone who mattered to her.
Her magic beverage is awful and sour, because her enchantment if flavored by Guilt.
Her assault plan is full of holes by general inspection. She IS taking HUGE risks right now, to test if she could lay down her burden properly before dying. Even though she has survived this before, she knows what risks she takes fighting solo, but the risks don't matter anymore. I think defeat in combat could be acceptable in her view, if the opponent was morally superior and vastly capable, and would solve her one big issue(insert issue here.) Not that I want us to do that.
Rionna is being manipulated to remove us, since she is an extremist with one (public) interest (grief movers) and poor social skills. There may be a person in Tokyo who would rather not investigate what we are and what we mean. Rionna simplifies the world for that faction, if she freely kills us. They gave her a slanted report. Rionna has no care of this ATM.
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Actionable ideas?
Wait, we can offer a freebie to get the ball rolling.... Ask if Rionna can read the writing of witches. Tell her we can simply teach her in this room tonight. This would be simple, and not prone to blowback on us. It also makes us look really authoritative. "What, you don't stop and read the signs inside the barriers? I can." It is an ideal test to see if she has a fallen loved one?
Hunt a witch together, as a way to demonstrate our morality and power. Our theory of De-witching can be shown, rather than discussed. Our power allows a level of safety in a barrier that just doesn't happen too often.
Instead of leading with "give my morality a place over yours," we could make a legendary challenge out of this, and save someone to boot.
Let us propose to "do her job," as an apprentice. We were going to have to do something like this soon anyway to the Iowa girls.
Next time she gets a mission, she call us out too. We resolve it and protect the peace with our power, not hers. Be her flaming sword of justice.
Let her play at being Batman out on the periphery, in case we don't win. It doesn't bring us to her keep, and it is definitely contributing to her cause. We will be achieving our cause as well. Every time we go out with her, we may have to imprison some girl. Rionna only targets the murderers. But the criminal won't become a shade, even if she fights to the death.
"Chekov's" sparring DVD - is that why it exists? Is it a resume?