"Petit Eva First" is a comedic spin-off of the popular "Neon Genesis Evangelion" franchise, reimagining its characters and themes in a lighthearted, chibi-style format. The series parodies the original's intense and philosophical narrative, presenting a more whimsical and exaggerated version of the Evangelion universe. The story revolves around the daily lives of the NERV staff and the Eva pilots, who are depicted as children or in comically exaggerated roles. Misato Katsuragi, the operations director, often struggles to manage the chaotic antics of the young pilots, Shinji Ikari, Rei Ayanami, and Asuka Langley Soryu, while Gendo Ikari, Shinji's father and NERV's commander, is portrayed as a bumbling yet still intimidating figure.

The plot consists of episodic, self-contained stories that focus on humorous situations rather than a continuous narrative. These include the pilots attending school, engaging in absurd training exercises, or dealing with everyday problems like cooking or shopping, all while maintaining their roles as Eva pilots. The Angels, the primary antagonists in the original series, appear as quirky, often comical foes that the characters must confront in exaggerated battles. The series also incorporates meta-humor, breaking the fourth wall and referencing the original Evangelion series, as well as other pop culture elements.

The characters retain their core traits but are exaggerated for comedic effect. Shinji is portrayed as overly timid and prone to overreacting, Rei is aloof and robotic, and Asuka is brash and competitive. Misato's love of beer and casual demeanor are amplified, while Ritsuko Akagi, the head scientist, often finds herself exasperated by the absurdity around her. The series also introduces new characters and reimagines minor ones, adding to the comedic dynamic.

"Petit Eva First" is structured as a series of short, fast-paced vignettes, with a focus on slapstick humor, visual gags, and playful reinterpretations of the original series' iconic moments. The tone is consistently lighthearted, aiming to entertain fans of "Neon Genesis Evangelion" by offering a humorous contrast to its darker, more serious themes. The series does not delve deeply into the philosophical or psychological elements of the original but instead embraces its role as a comedic parody, providing a fresh and amusing perspective on the Evangelion universe.