The guy from the Plain Love one-shot is really a younger Shigure.So first of all: Kagano from the one-shot, who is supposedly plain, is definitely a Hollywood Homely. If you took his glasses off, he'd look like Shigure with less kempt hair. Shigure's current personality being different from Kagano's can be explained by his relationship with Wakana. Remember how Shigure makes slightly offhand remarks that his perpetually happy face is his facade? He broke up with Wakana because she did something that rendered their romantic relationship irreparable, which in turn is because she is not as stupid as she seems to be. His mother divorced his father and remarried. His stepfather's job as a hospital director causes Shigure to transfer schools and his personality changes into the personality we know in the series (because he made some vow never to be fooled like that again or something). He also made a promise to deal this retribution to the girls in his new class. He ditched the glasses for contacts and became who he is today.
This is really a shonen seriesIt would explain all the female ecchi.