Yuki Yoshida, professionally known as Maelstrom and nicknamed Tomonori or Yukinori, is a vampire ninja fighting against Seraphim's clan. She attends the same high school as Ayumu Aikawa under her Yuki Yoshida alias. Orito dubs her Tomonori based on her alias's kanji, a name she initially finds too formal and dislikes, except when Ayumu uses it. Haruna calls her Yukinori. She has blonde hair often tied with a ribbon on the right side, stands 168 cm tall, and possesses an E-cup bust size which she unintentionally exposes. Her personality starts as abrasive and confrontational, marked by using masculine pronouns like "ore." This demeanor shifts dramatically after an accidental kiss with Ayumu, triggered when Haruna pushes him into her. Following vampire ninja custom, this lip contact signifies marriage, a bond she fully embraces. Post-kiss, she treats Ayumu as her husband at school, preparing him homemade lunches often ruined by excessive sauces. She seeks romantic advice from friends Taeko Hiramatsu and Kanami Mihara. Her devotion deepens when Ayumu saves her from losing control of Mysticore, a giant flame spirit residing within her that rampages if her consciousness falters. She later interprets a ring he gives her to suppress Mysticore as a wedding band. She grows jealous of other girls interacting intimately with Ayumu and attempts to kiss him while he is comatose, though Haruna stops her. Her abilities include deploying tonkotsu ramen soup to defeat Megalos, though she doesn't understand how it works. She initially uses a citywide ramen-spraying machine against Megalo hordes, later destroyed. She also performs curse dances—called "voodoo dances" by Haruna—that induce suffocation and force others to dance involuntarily. During Season 2, chosen as a backup dancer for Sarasvati, she accidentally performs this curse dance, leading to unsuccessful intervention by Haruna and Ayumu. Her critical power involves hosting Mysticore; its emergence risks catastrophic destruction unless contained, as when Ayumu halts a rampage with a cooldown hug. In the light novels, her relationship with Ayumu extends beyond the main series. After he reverts to humanity and becomes a salaryman, she secretly meets him for adult encounters, contrasting his diminished assertiveness towards other female characters.