Brief overview of Geno’s childhood.
Geno's dad was an abusive, neglectful being who refused to believe his son was not immortal and therefore beat him to near-death on multiple occasions. Geno lost it when the mother was murdered, she was the complete opposite of his dad and very much is the reason he survived childhood.
For clarification, Kenneth Slugfalls is not his birth name. Geno is just a nickname after he started following through with his plan. So, what, pray tell, is his birth name? No one knows. According to records, a child matching the one in Geno's childhood photos (Geno himself, but way smaller, weaker, and more colorful) ran away from home and was assumed to have promptly died due to neglect and malnutrition. As well as his younger brother, who escaped the situation years before the murders, Glug Titrate from Energetic. The brother was also born differently than his adult form. More on him later.
Geno Slug's father was a partial eldritch who was 100% power hungry and wanted his kids to grow up "perfectly" just like he couldn't.
Which... In the father's flawed mind meant doing everything in his power to make sure his family knew that he was in charge. And whatever he wanted, he got. If he wanted to break something, he broke it and no one was allowed to tell him off for it. If someone else broke something, rule or otherwise, he punished them how he saw fit. Sometimes he'd just hurt someone for the fun of it.
Geno's mother was completely human. She had good networking skills, access to healers of all kinds. Regularly, she'd have friends over while her husband worked. She loved her husband, very dearly, so she never said anything about his abuses. To her, it was just him trying to show love the way he was taught as an eldritch child.
The mother was Geno's one friend. Best and only. He relied on her for everything. The food she cooked, the comforts she gave, the doctors she called in to heal them, the clothes he wore... Oftentimes, the three could be found sitting in the living room cuddling in the silence until the husband got home.
That is, until the father went too far. He took the mother’s life away, and in return Geno took his. He fled home, with just the clothes on his back. Fear and adrenaline coursing through him. The shock of what he'd just done, the grief over his mother...
After a few hours, he felt that sense of control he'd been after all his life. Developed this belief that all eldritch creatures are evil. Realized he liked killing, as well, and thus his criminal spree began.... He stole, lied, manipulated, did whatever he could to get himself on his own feet. Independent from all sources save himself and his own interests.
His whole plan centers on avenging his mother and brother, spiting his father, and preventing others from suffering at the hands of eldritch creatures...