
yeah exactly, it isn't a story about dolphins, otters or any animals, they're human like characters put into rather human society settings (for example where they form families and have sibling to sibling relationship) so I think human morals and social rules still applies in this case.
it is true that rape occurs very often in animal world which is interesting and also lowkey terrifying fact but I don't know to what extent you can actually justify the character's action and say it's just instinct
anyway, it's really fascinating topic of how much animal behaviours you can give your humanoid characters
so he raised him like a brother and then they fucked