Ok first is Seto no Hanayome. I've only read a little of the manga because I watched the anime first.

The story begins with middle schooler Nagasumi going to visit his grandma. He "decides" to take a swim in the beach and finds himself drowning without anyone to help. Just before he passes out, he sees a mermaid come to his rescue. He wakes up to find himself alive on the beach. He tells his whole family about what he saw but no believes him. Everything changes when the a cute girl who looks exactly like the mermaid who rescued Nagasumi arrives that very night and in front of is family, tells him to "take responsiblitiy for what happened that afternoon."

The anime is extremely funny to me and a real good stress killer. I think the manga is the same as the anime but if you watched the anime first like me, the manga art would kinda surprise you. There's not much cons for anime/manga except that it could get kinda corny and times but other than that, it's very entertaining.

Read it on onemanga and see what you think.