My Bride is a Mermaid - Season 0 Episode 2 Gi

The first half of the episode has Shiranui working in a maid cafe to pay off the damage she did to the store. Sun, Mawari, Satori and Lunar offer to work there also, and a 'competition' begins between the four. At the end, the store is destroyed again. The second half of the episode starts with a flashback scene from when Sun was a child, playing with her friend, and they make a promise. Then, Lunar and Nagasumi are watching a horror movie in the house while the others are out. Lunar freaks out and a zombie girl appears in the house. A few things happen, and the so-called zombie girl tells Nagasumi that 'It's all your fault.' The next day at school, she appears again and attacks all of the students except Lunar, who cowers in the corner. Sun returns and finds that the zombie girl is her childhood friend, Saturn. Saturn leaves, and they make a promise once more.