オトカノ ～おとうとの彼女が文系で強め!?～

It’s a summer night. At home.
After six months of dating, I finally cross the line with my humanities-major girlfriend.
After going at it multiple times, we fall asleep, wrapped in each other’s warmth.

The next morning, I wake up to a strange, ticklish sensation between my legs.
Blinking away the sleep, I look down to see someone fondling me with a dazed expression. But it’s not my girlfriend—
It’s my always-stern, overly-serious, science-major… older sister!