The “Bans” refer more or less to a series by Kajishima, and are the continuation after the OVA. Certain ones are named to reflect which storyline they’re focused on (ex. Tenchi bans are for main cast, GXP for the GP, Sekishi for Geminar).
Being doujins, they are very brief in nature, so you’re seeing all there is to see even if it seems really short or nothing really happens (they’re very slice of life, and as you’re likely familiar with, are often more or less pornographic in nature, so it’s just fan service).
