All of this! Everyone is so used to herms, futas, dickgirls, etc now that they gloss over the fact that it wasn't that normal in the in-game universe at all. Even in-game by the 'now' of the game people are pretty much fine with it and it's a more common thing (see Cotton) but it def didn't start out like that (see Urta).Well, she has an excellent reason too, they are a sign of corruption and impurity in the world caused by the demons. Demons who killed, fucked, corrupted, and destroyed her entire people and way of life to the point that the only other survivor is your mouse monk, Jojo. She hid for a long time and had to survive in a harsh corrupted land and at the same time keep her corruption to a minimum and use a little alchemy plus her survival skill to make it through. Then your ass strolls in possibly holding the key to reviving her people and you being a (possible) herm would obviously bring some and shit. It takes YOU talking to her, getting to know her and shit just to break down her walls and for her to become close enough to YOU to have children and revive her race. Then later can move in with YOU to your camp. She isn't and should not just jump on someone's dick in the first five fucking minutes of finding out about them, character development is a thing and Amily isn't precisely easy is the Fucking point. It is especially dumb considering how she reacts to Marble and Izma so she is not going to hop on a random dick she talked to for an hour.
TLDR: Fuck off with your shit justification for that threesome and don't ignore character development.Oh and don't fucing be surprised people would be annoyed that someone fuck gets to fuck something on the first a 8sec of meeting them when the player actually has to do shit to get the ball rolling.