Otonari no Tenshi-sama ni Itsunomanika Dame Ningen ni Sareteita Ken S01E03 - Reward for the Angel

Amane's mother, Shihoko, arrives at the apartment without warning while Mahiru is visiting. Amane asks Mahiru to hide, but Shihoko eventually finds her, and the two neighbors frantically try to correct Shihoko's assumption that they are dating. Nonetheless, Mahiru is touched by Shihoko's motherly kindness. After Amane sees how happy Mahiru is to be called by her first name, he tries calling her "Mahiru" too. From that day on, the neighbors call each other by their first names.