Yumi's choice of a petite soeur isn't about plot, it's about becoming the person Sachiko already sees in her. Season 4 strips away spectacle entirely and asks what it costs to be trusted with someone else's growth. The Lillian Girls' Academy feels lived-in because these characters have been becoming themselves for three seasons already; this one just lets you watch it happen.

At Lillian Girls' Academy, life carries on for the members of the Yamayuri Council as another school year moves forward. A year after she and Sachiko became soeurs, Yumi is handed a hard assignment by Sachiko: she must at last choose a petite soeur, a younger sister of her own. The council is also working with the all-boys Hanadera Academy on a stage play, and the school festival is drawing near. Two new helpers, Kanako and Toko, join the council's work, but the pair do not get along, and each looks like a possible choice for Yumi. As tasks pile up and the expectations of Sachiko and the council grow, Yumi faces mounting pressure to make up her mind in this slice-of-life drama.