Sumire Miyazaki

Sumire Miyazaki is a minor character in Happy Sugar Life. She is Satō Matsuzaka's next-door neighbor and co-worker who refers to her as "senpai." Among her friends, her nickname is Su-chan. Sumire is a self-conscious girl, referring to herself as plain and awkward and idolizing Satou for being the exact opposite of herself.

(Source: Happy Sugar Life Wiki)