Йошіда Юкі

A vampire ninja from a different faction from Seraphim's who is also a student in Ayumu's high school. Maelstrom is able to use tonkotsu ramen soup to instantly defeat Megalos, though the explanation behind it is too advanced for even her to understand, and has a machine which sprays said soup over the city whenever a horde of Megalos attack. As a result of accidentally kissing Ayumu when he was pushed by Haruna, they are technically declared married by her faction's customs, and she constantly acts like a wife while at school, where she goes under the alias Yuki Yoshida. Because of how this name is written, she is nicknamed "Tomonori" by Orito.

In Episode 9, when Ayumu risks his life to save Maelstrom from 'self-destructing', she seems to have developed feelings for him.