Tales of Wedding Rings, Vol. 10 (manga)

Having been tempted by the Abyss King's retainer, Hime is trapped insidethe Sorcerer's Spire. In the spire, which has taken the form of the world insideher heart, Satou encounters various versions of Hime and is asked a mysteriousquestion. As the true nature of the dark heart which captured Hime growsgradually clearer, Satou makes a big decision...