Keiji Saga is the producer for Saga Entertainment, though he seems to be similar in age to Daisuke.
Saga is very energetic and shows little regard for the personal space or privacy of others; he occasionally gets called a pervert for it. He also seems to have an obsession of sorts for Daisuke. When Daisuke needed to try on the outfit for the commercial, Saga tried to undress Daisuke himself, and started to take off his own clothing in the process, before being stopped by Funabashi.
He first appeared in volume 3 of the manga, when he sent some of his employees to kidnap Daisuke in order to ask him to star in a commercial.
He temporarily transferred to Daisuke's school in order to oversee the Ice and Snow play.
He seems to be able to feel when Dark is in control of Daisuke's body ("Where's that aura of his that makes me wanna just jump on him?!") and later on, he also suspected Daisuke of being Dark. He followed him around for a while in an attempt to prove this. However, he was fooled when With transformed into Daisuke at the same time Dark was stealing an artwork.