These are known as Itachari (痛チャリ) and can usually be seen dotted around Akihabara.
痛 (ita) = Pain
チャリ (chari) = Bike
It is a bike with anime, manga, and video game characters decorating usually the wheels. The decorations usually involve paint schemes and stickers or coverings on the wheels. These characters are predominately moe females.
Anime characters. It's called itachari..