I honestly don't get why so many people have a problem with them being second cousins, or why they think this is illegal? It's not like you could help who you fall in love with. Is it the age gap? It is, which is why I think it doesn't matter even more. It's consensual and if Kyuuta doesn't want it, he can - very painfully - make that clear to Etsurou. There is no problem, at all.
Oita ga Sugiru wa Koneko-chan