Len's just slightly less girly than Miku, and Rin probably forced him into a bikini. (You wouldn't get tanlines just from wearing a bra unless you were out in something *really* sheer or *only* a bra). That, or the artist prefers to think of him as a girl. He's close enough to go either way, poor guy.
Personally, I subscribe to the 'Rin forced him' camp. He's her bitch.
Tako-Kaito nosebleed made water red. xD Nah! Just the soap... :P
By the way... Kaito "cosplaying" Tako-Luka just to get into bath while girls are in (ignoring Len right now, just for his bra print Dx ) just to have a good time? Kaito scores! :D