Ohm is the first son of Vieg and Vahti. He is mostly a background character, but serves as the main focus of Chaos Rings Ω and Vieg tries to rescue him from Cyllis, who wants to kidnap and experiment on him. He also appears in in the Extra Mode of Omega. Ohm is also mentioned in Chaos Rings, chronologically after Omega, and it is revealed that he died a long time before the events of the game, as he was not given Immortality like his parents.
By the time Vahti is transported to the ark, she is already nine months pregnant with Ohm. Shortly after reaching the Ark, she gives birth, right before the first battle between the different pairs. The protagonists win her some time to give birth and, with their help, she gives birth to Ohm. Ohm remains in Vahti and Rachell's care during the battle between Vieg and Dante, but during or after the battle Rachel is killed by Cyllis, who then kidnaps Vahti and Ohm (she specifically wants Ohhm because he is a "valuable specimen", the first human actually born on the Ark). Ohm is later returned to Vieg by Yorath and placed in Piu-Piu's care, but is later re-captured by Cyllis.
Dante manages to recover Ohm and Vahti, at the cost of his own life. Ohm is again placed in Piu-Piu's care, and Vieg and Vahti take him with them through the Original Door after defeating Cyllis's first form and the Dante & Rachel hybrid. However, they are all trapped in a collapsing timespace on the deck of the Ark and forced to fight Cyllis's final form. Ohm is present during the battle, but does not get injured, nor does he obstruct his parents' battle capacity in any way. At the conclusion of the battle, Yorath teleports Vieg, Vahti and Ohm back onto the Ark, and they later end up on the Earth 10,000 years in the past after using the Original Door again. Although Vieg and Vahti are initially uncertain about what to do next, they cheer up after seeing Ohm smiling.
In this storyline, Vahti already gave birth to Ohm before being transported to the Ark. Ohm is in Piu-Piu's care for the entire storyline, and the player can buy items for him, such as toys and milk. Buying enough items for him will produce the most powerful weapon in the game, Creator (Ohm) and also the Viper Revitalising Drink, which is required to fight Piu-Piu's final boss form.
In one of the collections revealed, with a implied image of Escher, Rachel notes some similarities between him and Ohm
As Ohm is not immortal, unlike Vieg and Vahti, he eventually dies a natural death long before the events of Chaos Rings. Vieg and Vahti still remember him as their first child and he is briefly mentioned by Vahti's clone.
In-game, Ohm's name originates from "the language of ancienct Ezcar". In the real world, Ohm's name is probably from German physicist Georg Ohm, who is responsible for discovering Ohm's law. Incidentally, the unit of measuring the resistance of conductors in physics is also named an ohm after the physicist, and is represented by the Greek letter Ω. Thus, the title of Chaos Rings Ω could also be read as Chaos Rings Ohm.