Immediately after the death of Paratice Head, Optimizer appeared and began to spawn smaller, common D-Reaper agents. Gallantmon and Justimon fought Optimizer, but were at a disadvantage to its underlings. Gallantmon tried to reach its head to weaken it, as he couldn't get at its giant cord connecting it to the D-Reaper, but was unable to get high enough.
Then, thanks to Yamaki, the Monster Makers, and, in the end, Gallantmon himself, Grani the ark bio-emerged, becoming Gallantmon's steed, which he rode to Optimizer's head and impaled its neck with its spear, weakening it and allowing him to sever its cord with his spear, destroying Optimizer.
Later, during the final battle with the D-Reaper, another Optimizer was created, but was easily destroyed by Sakuyamon with Amethyst Mandala.
Optimizer can spawn smaller D-Reaper agents, which are sent to attack its enemies and protect its weak point.