Ashmodai
Why is he doing a canon rehash? Dude had devil magic, teleport to the chess room, put. Soul trap and eat the soul of Voldemort, remrmber that devils can do it, they just stoppped making deals for souls because of bad publicity, the deals are good enough to slowly increase power, but a soul is a pretty good power boost, And why has harry not been in contact with Rias? Rember that if he stays too long separed from her, his own demonic power will corrupt him and transform him into a stray devil, Proximoty with Rias acts as a stabilizer agent, for a time period (i think it was 10 years) or he becomes high level devil and his demonic power stabilizes, finishing his trasformation... Other than that good chapter... (I REALLY HOPE that you dont try to copy the ending of book 1, where Voldemort in soul form passes through Harry, because if he did that here, he could 1 be destroyed by demonic power, 2 automatically eaten by Harry's devil physiology or 3 easily captured by Harry, either by hand or his sacred gear, no matter how "surprised" he is)