Mata Ashita to Iwasete

On the way home from a workplace drinking party, Mazumi bumps into a boy. Wanting to get away from the situation as quickly as possible, he lies and says the boy is her relative, which leads to the two becoming involved... A cold-hearted young man and a boy who tends to expect things - their days begin to take on color after this chance encounter.

(Source: Ichijinsha, translated)