Chujin is extremely distrustful of humans, viewing them as the continual oppressors of Monsterkind. To defend his species from humanity, Chujin created the Axis line of robotic Royal Guards, hoping the Kingdom would adopt them as a soldier force. Unfortunately, it took numerous models to refine Axis, and one failed prototype burned King Asgore's flowerbed, causing him to be fired from the Steamworks.

Chujin's distrust of humans was greatly intensified when his daughter was threatened by a human attack in Snowdin. Shook by the possibility that his daughter could have died in that attack, Chujin spent the next few years researching a way to make monsters themselves strong enough to fight and defeat humans, as by nature, monsters are far weaker than humans. His theoretical serum for doing so involved combining the essences of human and Boss Monster Souls. Due to the rarity of Boss Monsters, however, he repeatedly experimented on himself, which ultimately cut his life short. On his death bed, he tasked his wife with continuing his research.