Tsugumomo
Tsugumomo is one hell of a manga, it has ecchi, it has a good enough plot, comedy that actually works, characters that are actually likeable and get development, enough mystery to keep the readers hooked in. But sadly, this isn't talked about much.

Also, the concept is just SO GOOD. It also has a great power system, that actually makes sense. I don't know why people don't talk about it even though it has 2 anime seasons. It's a mystery to me till this date.