When Kanna was adopted by her parents, Kugie made her dislike for her very clear, leading for Kanna to run away from the household at one point. After Kugie found Kanna with a boy, who she presumed was teasing or picking on her, they began to fix their relationship.

It's implied through Kanna's self-introduction that they became closer over time and spoke to each other more. It's also implied that she trusted Kanna highly enough to save her in their first trial, though this later showed to fail through Kanna's panicking.

One day Kanna couldn't take her sisters bullying any longer so ran away from home, sitting in a park with a bucket on her head. Kugie had looked for Kanna and finds her with a boy who she misunderstood to be teasing her. When Kugie took Kanna back home they began to fix their relationship and started to get along. 

Kanna and Kugie were walking home one day, eating ice cream and talking about what to have for dinner, when people had jumped out from a black car parked across the road.

When they both woke up they began their first trial, "The Two Person Vote", where both her and Kanna were strapped down to beds and given a time limit of five minutes to escape. Kugie gave Kanna the key, allowing her to set herself free, but became panicked when she didn't know what to do resulting in Kugie's bed folding and thus crushing her to death.

A phone is later found in Kanna's and Kugie's first trial room with a message of hatred wrote on it. It was decoded to be a falsely wrote message soon after it's discovery, however.