An Aunt After My Own Heart

Discovering his beautiful young aunt is engaged to be married, a nephew takes matters into his own hands.

The protagonist, Keisuke Shinozaki, returns alone to his grandparents' house to stay for summer break.
There, he is greeted by his mother's (much) younger sister, Yuuka.
Ever since he was little, the protagonist had always adored on his kind, smart, and beautiful aunt.
However, it was quite the shock to learn that she was now engaged...

In "Longing and Guilty Pleasure", the protagonist confesses his feelings to his aunt, unwilling to hand her over to anyone else.

In "Regret and Lust", the now-older protagonist decides to steal her back, in spite of the blessing he'd given to her marriage years earlier.

These two stories follow the transforming relationship between nephew and aunt.