[MIMK-282] My sister-in-law believes it’s her duty to handle her stepbrother’s sexual needs.

After his father’s remarriage, a boy suddenly gains a new stepsister, Chiaki, the most popular girl in school.

Chiaki has fully accepted her mother’s hometown custom that a stepsister must handle her younger brother sexual needs.

After school she spots his erection, teases him with a mischievous smile, and immediately takes him into a stall in the boys restroom.