"Trinity Seven" is a fantasy anime series centered around Arata Kasuga, a high school student whose ordinary life is upended when a mysterious phenomenon known as the "Breakdown Phenomenon" destroys his hometown and causes his cousin, Hijiri Kasuga, to disappear. In her place, a grimoire manifests, granting Arata immense magical power. Determined to uncover the truth behind Hijiri's disappearance and the Breakdown Phenomenon, Arata enrolls in the Royal Biblia Academy, a school for mages, where he encounters the Trinity Seven—seven powerful female mages, each representing a different magical archetype.

The Trinity Seven consists of Lilith Asami, the Mage of Rage; Arin Kannazuki, the Mage of Envy; Levi Kazama, the Mage of Sloth; Akio Fudou, the Mage of Pride; Yui Kurata, the Mage of Gluttony; Mira Yamana, the Mage of Lust; and Lieselotte Sherlock, the Mage of Greed. Each member possesses unique abilities and personalities, and they serve as both mentors and rivals to Arata as he navigates the complexities of the magical world. Arata's carefree and flirtatious demeanor often clashes with their individual quirks, but his determination and latent potential earn their respect.

As the story progresses, Arata learns that the Breakdown Phenomenon is linked to the collapse of parallel worlds and the emergence of powerful beings known as "Demon Lords." These entities threaten the stability of the multiverse, and Arata's newfound powers position him as a key figure in the conflict. The series explores themes of identity, sacrifice, and the nature of power, as Arata grapples with his dual role as both a potential savior and a potential destroyer. His journey intertwines with the personal struggles of the Trinity Seven, revealing their backstories and motivations.

The narrative is driven by a mix of action, comedy, and supernatural intrigue, with Arata and the Trinity Seven facing off against various antagonists, including rogue mages, demonic entities, and rival factions within the magical community. The series balances its darker, more serious moments with lighthearted humor and romantic undertones, particularly in Arata's interactions with the Trinity Seven members. As the stakes escalate, Arata must confront his own limitations and the moral ambiguities of wielding immense power, all while striving to protect those he cares about and uncover the truth behind Hijiri's fate.