When Gretel was asleep, Hansel wasn't. The witch was sneaky. She knew who they were, so she poisoned the food. Not with actual poison though, she used spells. The ones used to turn humans into witches.
Hansel saw all of it, for the witch only did it when Gretel was asleep. He would see and hear her spells, but never know what they meant. This was every night. Being there for two weeks and not being able to tell Gretel anything was miserable.
The witch had finally told him what her plans were, but it was by accident. She had been working on the candy and assumed that both children were asleep. Gretel was asleep, but not Hansel. She began talking to herself about her plans for the boy. He was going to kill her sister.
Hansel was beyond terrified.
When he set the witch on fire and saw his sister looking proud, he knew he couldn't tell her. She would be afraid.
A week after escaping, he became ill from the witches spells. He was beginning to decompose. He needed a solution, and fast. He went into the market and found anti-witch medicines. He bought them and began using them. He soon realized that one would not work, so he began to time how long they would last him. The lasted eight hours every time. He then made a timer to tell him when to inject.
Gretel had asked him what he was injecting himself with. The only answer she ever got was that he was sick from the candy. It was the truth, but only half of it.
When they were eleven, Hansel thought of telling her about his condition, but she only wanted to rid witches from the world. The thought was immediately thrown out of his mind.
Together they began killing witches and saving children.
Gretel was always very good at it, but Hansel was better. He only did better because he felt that if he wasn't, she would think he didn't want to kill witches. That could lead her to the truth, so he always did better.
Years later, he still kept it a secret. The secret he always worried about.
Now, he knew that no one would ever find out, until they fought the Witch of Secrets. The Witch of Secrets could see your lies and fed off them. She could see every lie you have ever told just by looking in one's eyes. She was also a grand witch.
Hansel's world was about to drown him in front of everyone.