Character: Erika Kazama Flick 483f6u

Erika was adopted into the Flick family when she was a toddler. She grew up with Keith and attended some of the same schools with him.

During that time she met Gilbert Ross and the two of them became friends. However, Gilbert developed feelings for her, and was shocked to discover that Erika had romantic feelings toward her adoptive brother, Keith. Out of shock, Gilbert kidnapped, tortured and murdered her by slicing up her body. He then dumped her body in the mountains where it was later discovered. Her murder became the driving force for Keith's hunt for her killer, 8 years later.

Despite being dead, Erika's presence still lingers in the minds of her loved ones. She is very much the cause for Keith getting involved with the Killer B cases and Gilbert still speaks to her now and again as a ghost./spoiler]

Source: B: The Beginning Wiki