Fire Emblem: Three Houses - Fishing Shirts

There is more to them they being gay. Gay isn't a character trait. the sexuality as no bearing on anything. The jokes here isn't that their gay it's that the professor is a great fisher and Edelgard is happy that she is the best catch. The joke works the same if the professor was male or female. It's just a fishing pun.

The internet needs more 25 year old fishing boomer Byleth.