Persona 2: Innocent Sin
Eikichi is a second-year at Kasugayama High, the rival school of Seven Sisters. After the incident with The Joker, Tatsuya, Lisa, and Eikichi form a group to go after The Joker.
In Persona 3, Eikichi has a small cameo. On 11/16 if the player watches TV in the lobby there will be a show on talking about a chef/rockstar with blue hair and strange make-up and how yesterday was his birthday, this is a references to Eikichi.