Let's go, Ume-chan! Attack from a standing position!?

Ume-chan, who was called out unexpectedly, secretly tries out the cowgirl position at school after classes… Ume-chan, who has excellent athletic ability, works hard and serves him. Gradually, Ume-chan gets used to it. Soon, she can no longer control her sexual desire and starts to act more intensely on her own… ​