Umaru's Onii-chan is the seventh episode of the Himouto! Umaru-chan anime series. It features Taihei waiting on Umaru around the house, and accidentally throwing away a Hatsune Migu box that, despite Umaru's permission to throw it away, she actually really wanted. Umaru starts guilt-tripping him for doing so (so her brother won't be able to yell at her for anything). Taihei then looks everywhere for the box, ultimately going out to find her a replacement, leaving Umaru feeling lonely and looking for him.
In a later segment, Taihei goes drinking with his colleague, Bomber, who eventually demands to go home with Taihei, hoping to meet the girl he has heard so much about.
In the final segment, Taihei gets lost on his way home. He knows he has been down these roads before, but cannot remember when or why. An encounter with a local cat eventually reminds him when he was last here, and he experiences a flashback to his childhood, when he also saw a cat (possibly even the same one) while walking home from school along this road with his mother.