Shishunki no Obenkyou

Puberty is a time when many become interested in the opposite sex for the first time, but Kasuga is hit more than most. She becomes so obsessed with thoughts of penises and balls that her grades are affected. Thus, when her childhood friend, Kobayashi, bets her that he will have a higher score on the next test, with the winner being able to request anything from the other, she sees her opportunity to witness male genitalia in the real world.

1-7. Shishunki no Obenkyou (思春期のお勉強, Puberty Study Session); COMIC Shingeki 2019-01, 05, 08, 12, 2020-05, 08, 11.
8. Onee-chan ni Makasenasai! (お姉ちゃんに任せなさい!,Leave it to Onee-chan!); COMIC Shingeki 2018-09