Dengeki Daisy follows Teru Kurebayashi, a high school girl who inherits a cell phone from her deceased brother. The phone contains a mysterious contact named "Daisy," who has been her brother's friend and promises to protect her. Teru relies on Daisy for emotional support, texting him about her daily struggles, unaware that Daisy is actually Kurosaki Tasuku, the cynical and reclusive janitor at her school. Tasuku, a brilliant hacker, secretly watches over Teru to fulfill a promise to her brother while battling his own dark past involving technological conspiracies. Readers enjoy the story for its blend of romantic tension, humor, and suspense, as the unlikely connection between a scrappy, optimistic girl and a brooding antihero unfolds through secrets, action, and heartfelt moments.