She can be very emotional and despite being shy, can be very bold with her attempts at getting closer to Takeo.
She's also patient and understanding, as she understands Takeo's relationship with was important to him and she even invites him to some of their dates and group dates so he doesn't feel left out.
She's kind and she doesn't feel right if someone does something for her, but she isn't allowed to return the favor.
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This form of familiarity may have allowed Yukiko to be comfortable enough to share her feelings for Suna, and to Rinko.
The romance was also pretty sweet and had a lot of lovable moments.