1x12 - Merman in My Tub

Wakasa gets nervous when Tatsumi is late coming home and gets out of the tub to look around the house, causing a mess and nearly drying out. When Tatsumi comes home, he thanks Wakasa for worrying about him, but makes him promise not to get out of the tub next time, or else he won't give Wakasa the cake he brought with him.