EVA-00 Kai is the upgraded form of Evangelion Unit-00 in the Rebuild of Evangelion film series, specifically Evangelion: 2.0 You Can (Not) Advance. It serves as a specialized, experimental Evangelion used by NERV and later associated with key battles against the Angels. As a modified prototype unit, it represents the ongoing development of Evangelion technology and plays a supporting combat role rather than being a central pilot character. Its presence highlights the series’ focus on evolving mecha designs and strategic warfare.