Elpizo was formerly known as TK-31, working in Neo Arcadian Bureau of Administrative Services. In his career, he discovered lots of secrets about Project Elpizo. Later, Neo Arcadia later turned their back on innocent Reploids, labeling them as Mavericks under Copy X's orders. In the meantime, before he could join his fellow Reploids in awaiting execution, a surprise assault from the Resistance interrupted everything. TK-31 with his best friend HE-22 flee the vicinity.
TK-31 starts developing hatred upon his homeland, waiting for a chance to retaliate someday, as revenge for all the sake of the fallen Reploids. Walking through the sewers, they talk about joining the Resistance, but TK-31 decides to first go to Area 7 to retrieve the Baby Elves (though he only obtains one). From that point on, he insists on being called Elpizo, all only for the future purpose of the assault.
After Copy X's downfall, Elpizo helps the Resistance build a more advanced new Resistance Base. He becomes Commander of the Resistance Forces through appointment by Ciel, as she wishes to focus on her energy research. Upon becoming commander, he begins planning "Operation Righteous Strike", as he believes the only way to save Reploids is to destroy Neo Arcadia. He concedes, however, that if Ciel finishes her new energy system, he will cancel his plans for her sake, although he's not convinced that her plan would work.
Elpizo kept on gathering soldiers and training them. Ciel desperately tries to dissuade him, but it only falls upon deaf ears. Several months later, Zero returns to the Resistance, totally a stranger to Elpizo. With his return, Elpizo feels bold enough to execute his beloved plans, which is ironically the only thing Zero wouldn't follow, believing that Ciel's method may have a chance.
About 40% of the soldiers were drafted, most of which were outfitted with cutting-edge weapons, their best sub-commanders and so on. The main objective was to deal a large blow as fast as possible in the main district, leaving a warning message from the Resistance as expected.
At first, the strike force dealt some serious damage to the land forces. However, the only thing that Elpizo didn't expect to fight were three of the Four Guardians. Created for the purpose of protecting the people and Neo Arcadia, they arrived after hearing the alarms. In short order, they turn the tides against the opposing forces, terminating every Resistance force seen in sight, having fought bravely to death believing in Elpizo's words. The mission was a complete tragedy, with no survivors and a big wound in Elpizo's pride. He, too, would have met his end had Zero not arrived.
Unable to deal with the loss, this was the point in which Elpizo started losing his sanity. He decided to leave the base and Ciel in command, leaving a message where he curses his lack of power as the reason he failed as a commander, so he decides to awaken the Dark Elf in order to completely wipe out Neo Arcadia and all of the humans, creating a "paradise" for all Reploids.
Even after releasing and absorbing the Dark Elf, he was still defeated by Zero. While dying, Elpizo apologizes for his actions, claiming if Zero hadn't defeated him he would have "done something unforgivable". The Dark Elf, possibly moved by Elpizo's redemption, momentarily reverts back to her Mother Elf form and transforms Elpizo into a Cyber-elf. Before he flies away, he openly states that the Dark Elf "wasn't completely evil" before disappearing for good. Unfortunately, the Dark Elf's reversion does not last long, and she escapes until found again in Mega Man Zero 3.