Frieren S2 E8 - The Opening

You missed that Genau did reach Stark and actually managed to bandage Stark's wounds with his coat. Managed to do all that with his guts basically out. And even with that Methode said it was almost too late when she healed Stark. So Genau likely did save Stark's life with that.

My interpretation of the young demon girl's fascination with humans is that it does serve a purpose for her. Her magic is illusion based. Understanding why and when humans do things helps a LOT with the success of her magic in the purpose of hunting humans.

Your assumption of Genau thinking of himself as a tool or cog is fitting since his name means "precision"

In another type of anime, Genau would be the morally grey and dangerous high ranking "ally" in the organization that controls the "magic system" of said world, but is sometimes antagonistic. I'm thinking sorcerer council in JJK, or any of the various shinigami in Bleach. Or even Bondrewd in Made in Abyss (not in attitude or degree of depravity, but in willingness to expend lives). Higher goals and ends justify the means type. If our protagonist was not a literal legend from history, we might have a far more terrifying view of Genau in the narrative. But with all that, as you say, complex and deeply troubled even.

Planting seeds indeed. But what tree shall grow? Only time will tell.

It's easy to miss, but Genau actually manages to read Stark and wraps him in his coat. Seems like a pretty good person to me. I don't really see the hypocrisy at all. He's a calculating person (utilitarian; the ends justify the means), but it goes against his instincts. Seems consistent to me. He's just lying to himself I guess. Methode calmly analyzing the situation while under pressure in a life or death situation is pretty impressive (and has some interesting parallels to Genau's detached disposition). Very few people can think like this and also execute a plan on the spot.

One thing i had not noticed on my first watch, the attack that Stark used on Revolte there at the end, is the same attack the demon girl used against him back in the Aura arc, when she was copying Eizen's attacks, and she hit stark and he said "your attacks bear no weight"...well now we have seen what that attack can REALLY do.

My reading: Genau falling for the demon impersonating a girl was prefigured by his checking for the demon's "son" in episode 6. He knows demons lie, but he looks, just in case, even though it's ridiculous. So, similarly, when Revolte threw that knife, in Genau's mind even the slimmest possibility of it being a human girl meant he had to act.

just when having dinner, naisu!