Boku-tachi wa, Koi wo Shitenai

A childhood friend invites the protagonist over with the line, "Wanna play at my place?" Using this as a password, the two engage in daily sexual encounters. She is small enough to lift her hips, completely absorbed in the pleasure of having a dick pushed deep inside her. Her small body has grown sexually, and she makes a prodigal face with every movement.

The two are unable to confess their true feelings to each other, but they communicate well through their bodies. He can't contain his excitement for this slightly sad and naughty situation.