She is present to see Fumi off for her first day at school. It is implied that she was a large part of Fumi's life in her old town. She is seen (in flashback) spending time with Fumi in her younger teenage years, such as teaching Fumi how to cook.
Despite Fumi's attempts to convince Chizu to spend more time with her in Kamakura, Chizu sombrely and apologetically declines, her motives for doing so becoming clear later on.
It is revealed that Chizu and Fumi have had a deeper side to their relationship, however, she neglected telling Fumi that she was engaged to be married. The shocking news later causes Fumi to avoid her cousin, stating that she is cruel.
She seems very flirtatious, as she often makes comments to make Fumi blush, and she has an air of mature feminine authority to her that her younger cousin latches on to; Fumi is palpable even to a smile from Chizu, and the older cousin seems to enjoy her control over Fumi. After the announcement of her marriage, Chizu appears to be deeply sorry and guilt-ridden for keeping it a secret from Fumi as she understands just how much the younger girl trusted her and sought confidence in her.
Chizu has extremely good relations with the Manjoume family as she even brings along her fiance to meet her aunt and uncle during a home visit. Fumi's mother seems to dote on her a little. It is never made explicit, but it can be gathered that Fumi's mother and Chizu's mother are sisters, as Chizu has a different surname.
While not appearing very much, it is quite clear that Chizu has had one of the largest effects on Fumi, being her largest source of emotional support before Fumi's move back to her old town.
Eventually Chizu stops visiting the Majoume family after getting married; close to a year passes without Chizu's appearance, possibly symbolising Fumi's growing emotional independence and self-assuredness as she no longer need her cousin in her life.
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