Mael Strom (メイル・シュトローム, Meiru Shutorōmu), or more commonly known as Yoshida Yuki (吉田 友紀) is a vampire ninja, of a faction opposing Seraphim's clan.
She is somehow able to dispel Megalo by covering them in tonkotsu ramen, a kind of pork soup, and even has a machinewhich sprays the ramen soup in a Megalo emergency, but was destroyed later. She doesn't understand it herself, saying in episode seven "I don't get the part about the super string theory either," but it seems very effective.
When she and Ayumu first met, Haruna shoved him into her, causing them to kiss. By vampire ninja law, they are technically married, and, at school she treats him as a husband, making him lunch and bickering with him. Ayumu doesn't seem to take it very seriously, but Maelstrom says that she's "always wanted to be married."