The Eminence in Shadow, Vol. 15 (manga)

Claire may have randomly disappeared (again), but at least she managed to find her own way back this time! What's more, her otherworldly experience has gotten the attention of Princess Alexia, who's increasingly worried that their school may hide a dark secret. The two team up to investigate, but they're not the only ones on the case, as both the Knights of Rounds and the Seven Shadows are pursuing the same leads...!