Kinokoinu

Hotaru leaves Kinokoinu at home with Itsuki for a night to attend an author signing event with Komako. Kinokoinu learns hiragana with Itsuki while Hotaru is away.

"Anzu bumps into Hotaru at the bookstore and ends up coming over to visit Kinokoinu. Anzu ""kidnaps"" Kinokoinu so it can meet Plum."

Turns out Plums is Kinokoinu's sibling formed from its spores. Plum lives with Anzu and her mom, Tsubaki. Tsubaki used to tease Hotaru in elementary school and is also a picture book author. Hotaru decides to get a cell phone after years of refusing.