well... it was technically experimenting with the third girls rather than cheating, AND Kiri-chan gave him permission to two-time her, so i don't see what's so wrong（￣へ￣）
its actually cheating that developed into an open relationship, first it was really just plain stupid on takeshi's part, second, i'd have to symphathize and can understand, whether it'd be experimentation or what, how would you feel if through out your life you have been cast aside standing at your sibling's shadow and find someone who thought they loved you only to be experimented on with also 2 other girls? just for the sake of him finding out what his feeling is? can i murder 3 innocent people just to find out whether still have my morality left? can i hit random children to find out wheter i feel anything at ll or not? is the fact that permission was granted AFTER i have done it excusable to the fact i have murdered in first-hand firs-choice? the thing is, the action has been done AFTER the permission, there's nothing left to say besides concluding it as cheating to open relationship another conclusion can be is that takeshi's an emotional manipulator
AHHHHHHHHHHH i hate how they always play off such serious topics, but then again it's jsut plain disgusting and not 'FUNNY" Him cheating was a serious thing to be discussed about, not with two, but THREE, FUCKING, GIRLS.