Let's get my guesses in, before the game comes out~
Level 1: Aki Sisters
Level 2: Kisume/Yamame
Level 3: Hina/Parsee
Level 4: Nitori/Momizi
Level 5: Yuugi/Rin
Level 6: Ichirin/Minamitsu
Level 7: Kogasa/Iku (lol random round)
Level 8: Sanae/Kanako
Level 9: Shou/Byakuren
Level 10: Satori/Utsuho
Level EX: Suwako/Koishi/Nue/Tenshi
Nazrin will be in th13, witch will be a Phantasmagoria game or replace Momizi.
Edit: Or put her into level 4 together with Nitori and Momizi because thats actually the Level that had 3 characters in StB... namely Reisen, Tei and Medicine.