Not much is discussed of Krixool's pre-M³ life, but it's assumed that he grew up similarly to Tyrontics. After a mech battle resulting in a draw for the two mech-slaves, the two form an intense rivalry, and eventually fall in love with one another. Caught kissing Tyrontics in Season 1, Episode 4, he and his lover were placed in front of Mr. Mech, who decided to taunt the two. Mr. Mech demanded that the two slaves fought to the death, but Krixool offered himself as a love slave in order to save the two in a desperate move. For reasons unknown, Mr. Mech accepted the offer, and Krixool hasn't been seen much since apart from short cameos after his capture. Krixool dies when the crew shoots a missile at Mr. Mech's City in the Sky.
Krixool is a kind and loyal individual from the little seen of him. He has much respect for himself and those he cares for, and was a skilled fighter at the arena with combat techniques specialized in trickery.
It's unknown how much of Krixool's personality changed when he became Mr. Mech's slave, because he only had limited appearances post-kidnapping.