An evidently shrewd young woman who is seemingly wise beyond her (apparent) years, and who associates with very few friends. Surprisingly, even though she resembles a diminutive 15 year old or perhaps younger, her real age is 21; her physical development was stunted due to her "standstills", in the same way that they affect Kei. She had been in a "standstill" for 6 years. Ichigo's loss of time and her sense of life cruelly having passed her by due to the illness (she wistfully reveals to Kei that she has a younger sister who is now married and expecting a child) tends to cause her to have a much more cynical and serious demeanor than is normal for someone of her seeming age, which is sometimes commented upon by her (much younger) friends.
In order to prevent the triggering of 'standstills', her emotional expression is very subdued and phlegmatic. But for all her apparent depressive state, she is in fact very caring, attempting to assist both Koishi and Kei by acting as a 'matchmaker' for the two, because her own losses have been felt so keenly, and because she doesn't want her friends to experience the kind of heartache she has felt by their wasting opportunities for closeness that she has been forced to endure.
She is quiet but fiercely independent, currently living alone in a rather Spartan apartment, partly on her own initiative so that her (well-to-do) family wouldn't be burdened by her malady. She still maintains ties to her family, providing at least a semblence of normality. At one point she confesses to Kei that had they met earlier and revealed their mutual affliction to each other sooner, they might have become closer.
Her keen mind causes her to suspect the too-often 'coincidences' regarding their former teacher's departure, the new one's arrival and strange events in their neighborhood immediately after that to be connected, but her much younger and guile-less friends dismiss those connections. She also deduces that Kei and Mizuho repeatedly being found together in unusual situations to be the result of a covert relationship, but does not alert the authorities, preferring to observe the situation to verify it, proving herself to possess a formidable intellect as well as no small degree of compassion.

In Onegai Twins, she has apparently changed a lot, ever since being elected as the Student Council President. Since then, she has shown a somewhat sadistic personality, perversely enjoying the sight of other people in trouble, especially her own schoolmates, while maintaining her phlegmatic personality.

(Source: Wikipedia)