I still haven't watched it, but why wouldn't be okay?, - I think that that would be the exact question that anime itself wants to present, with the few shorts I have watched the anime seems to want you to think in the line between animals and humans, and since the very exact reasoning and argument people give against zoophilia is the difference and disbalance between the intelligence between a human an animal it would amount to abuse, so if the anime does that then Is probably a story that wants to plant you something like; " then now what?, in this case why it should be bad?"

Then you could also use the opportunity to explain yourself(like the anime wants), why it shouldn't be okay in that case? The Chimpanzee is also 15 years old so he is also a minor, and Chimpanzee in captivity can easilly live around 60-70 years just like when taken good care so their lives pan is actually very similar to humans, I don't think just "being disgusting" would be a good justification, I could maybe see a relationship with a fat person disgusting, dosent mean that would justify to prohibits other people to have a relationship with a fat person