An Ultrakill OC/AU of mine. V1 had to be trained in combat with a training dummy known as V0 or the V-Teacher Model. They were even utilized to help V2 become an effective security machine during the New Peace.
They were later put away after the failure to sell the V2 model during the New Peace. They awoke years later, soon after V1 left, and followed close behind, scavenging robotic parts left behind by V1's destruction. They then crafted a staff that could shoot hell energy and the blue hell energy orbs to target enemies with.
Soon after the death of V2 in Greed, V0 makes a form of grave for V2 and mourns its death as V0 had grown attached to both of the V-models through their training.
V0 later meets with V1 in 7-2 in the final room of the level, instead of their being enemies or a maze, all of the pillars have fallen, and only V0 is in the room, surrounded by Gutterman and Guttertank bodies. They then bow and fight V1 using their staff to fight alongside being able to control the pillars of the room to try to crush V1 or to use it to climb.
After being dropped to 1 HP, V0 will surrender and kneel to V1, wishing for it to kill them. V1 can either choose to kill V0 or leave them to bleed out in the Violence layer. No matter what choice V1 makes, V0 will eventually die one way or another, and the student will become the master...
(The AU is not really fleshed out, and there may be some contradictions in the story and such, and I came up with it as a shower thought, so yk)