Some are useful other are not. The most useful is Selina.
Still, the harem is rarely an important part of the story, except the comic part, in many parts of the story the harem is not even there, even though women still feel in love with him.
To be honest, the characters personalities in general are great and is a funny and interesting story, as I said, the harem is second place in the story or for comedy, specially Sei jealousy, but he doesn't have an annoying harem!
Also, all his harem are women older than him!
Ohhhh I see (๑•ㅂ•)و✧ I might give it a try, thanks a bunch! ヾ(❀╹◡╹)ﾉ~
Is this worth the read? Are the ladies in his harem are useful like in the manga Re: Monster? Or just another harem that will ruin the story?