Shiori Tsukishima is a minor recurring character in the Midori Days series. She is a grammar school student who has a large crush on Seiji. Her age and crush on Seiji are typically the topic of her appearances.
Shiori's first appearance in the manga and anime differ.
In the anime, she appears to tease Seiji about not having a girlfriend, and offers herself as a girlfriend which only further irritates Seiji. She then appears in the following episode as Seiji heads to school. When Seiji hides his hand; Shiori assumes it is a pornographic magazine and teases him about that as well before taking off. In the manga, her first appearance is marked when she tackles Seiji and begins teasing him a little. This happens some time after the first several chapters.
Shiori reveals to Seiji that she is upset with her stepmother for trying to be her real mother, and then proceeds to reveal to the reader/viewer that her mother has passed (she never states what caused the passing of her mother). This reveals Shiori is stuck in a mental conflict with her caring stepmother who is legitimately trying to be nice and learn Shiori's likes/dislikes and behaviors to try and be her mother, and the memories of her biological mother whom she hasn't let go yet. This eventually continues until one night when Shiori is late at Seiji's home and her stepmother comes looking for her. When the stepmother shows up worried about Shiori and asks Shiori to come home, Shiori explodes in a yelling session where she begins making crass, unfair, and incorrect statements to her stepmother about how she just wants Shiori gone and that her stepmother can never measure up to her birth mother. This results in her stepmother slapping her in frustration and then breaking down in tears begging Shiori to just accept her and get along better. In the anime, the two forgive each other in the doorway and resolve the problem. Shiori tries to play off her stubbornness as "not wanting to leave Seiji alone", and then grabs her stepmothers hand and says she's ready to go home "mom". In the manga her stepmother returns home without Shiori and asks Seiji to watch her for the night, which leaves Shiori time to think about what she has done and this causes Shiori to realize her stepmother does care. The following day the two are seen shopping in town and are getting along like a daughter and mother.
Shiori makes multiple attempts to try and get Seiji's attention, and has even stated she is not interested in children her own age. She makes multiple attempts with Rin to try and win Seiji's attention by dressing up in several lightly fetishized outfits (school gym outfit, Chinese dress, dominatrix apparently made for a child sized individual) however these all fail spectacularly.