Huh, I always thought that Okuu simply left her shirt unbuttoned. Guess she gets them specially made
Genyoshko probably has a lot of specialists in modifying clothes. For example, Aya presumably buys regular shoes, and then has someone attach the tengu geta soles to them (which would explain why most of them still have the low heel in the back they would if they were normal, even though the geta platform makes that bit useless.)