Shissou Sengen

Ayumi Sakamoto, a 24-year-old office worker. She is serious, quiet, and simply spends her days working. Just working, eating then sleeping, with nothing to do on her days off; nothing new, just those repeating days. However after a reunion with an old classmate, she makes a decision. A manga about a woman who doesn't have a single fun thing in her life.

(Source: Tokuma Shoten, translated)