@KazumaLee94
He's just jelly that Sora is cool, and think that a cool guy fits Amano better than his nerdy ass.
It doesn't matter that Sora is Amano's cousin (2nd cousins can marry in Japan) or that Sora has a GF (that actually makes it worse) : Sora is in every metric superior to Manabu (in his mind) so he's thinking a guy like that would be suited for her more, but Sora specifically.
It's a case of "I want my beloved to be happy" causing jealousy
He's just jelly that Sora is cool, and think that a cool guy fits Amano better than his nerdy ass.
It doesn't matter that Sora is Amano's cousin (2nd cousins can marry in Japan) or that Sora has a GF (that actually makes it worse) : Sora is in every metric superior to Manabu (in his mind) so he's thinking a guy like that would be suited for her more, but Sora specifically.
It's a case of "I want my beloved to be happy" causing jealousy