The un-wanted (owari no seraph)

When yuu chan goes missing after being possessed by a demon Mika and yuus team mates goes on a jaw dropping journey to find there beloved yuu-chan!! But during a fight between the 4 horsemen of John and some unwelcomed guest's a stranger appears with there mysterious comrades to save the day! Will Mika ever find yuu-chan again? And when he does what will they do next?!