My Devil is a Beautiful Female

Roy Yagami, 16 years old. His goal, 'Become The Strongest'. His first step towards becoming the strongest is to Join the 'Knights'. But just before the Knight entrance exam, an incident occurs where an 'Unknown Being' enters his body. Not knowing what dwells inside his 'body', he tries to start his journey of trying to become the strongest. AKA 'The Supreme Being'