Usotsuki Mi-kun to Kowareta Ma-chan (Light Novel)

Years ago, a kidnapping incident left a pair of victims with lasting psychological scars: Maa-chan is prone to violent mood swings, while Mii-kun's pathological lying shrouds his life in mystery. Now, when the news begins airing stories of kidnappings and serial murderers, Mii-kun moves into Maa-chan's house, in an effort to protect this girl who he has been through so much with. But can he save her from herself?