It's a child. Please, no.
Omichi please stop falling for the literal child.
They're both children, you're overreacting.
When you're an adult, 5 of 10 years of age gap don't matter, but that's not applicable in minors. I wouldn't see with good eyes a couple of a 5 years old and a 10 years old, neither 10 years old and 15 years old. In minors, every year changes a lot and makes a difference of maturity. It's nor right, it's strange. It's obvious that Rin should be a lot less mature, and Omichi more.
I don't really understand why they treat the kid like it is 20 years old in all that conversations. It made me feel uncomfortable.
(Sorry for my poor English)