'Yoiko' is a classic (to me), hilarious, ecchi anime from the late 90s. The story is about Fuuka, an elementary school student that looks like a hot 20-year-old. So of course everybody mistakes her for an adult, which brings her into one funny situation after another. This idea inspired many other manga/anime from today.
Her female teacher wants to look like her, the young boys in her class fall in love with her, and then there's her perverted cousin (I think) Jiro who involuntary shares his bedroom with her, and feels cursed by the god of masturbation. Fuuka's mind sure is one of a child! Her unusual ideas and her naive soul is essential to the comedy of Yoiko.
The animation is nothing outstanding, but you do get some fan service, well mainly Fuuka in lingerie or naked under the shower lol. I just laughed through all episodes, every character is crazy and so is their behavior (especially the teacher's) and all of them make this show a happy meal for the audience, the eps. are rather short (10-12 minutes), but because the show is so funny it feels more like 5-minute episodes! So if you don't mind old school anime art (which I love), you will probably enjoy this, too. And although I say this is an ecchi anime, it's far away from being dirty. Give it a try!
