Our Last Crusade or the Rise of a New World, Vol. 5 (manga)

For years, Alice has worked hard to succeed her mother as queen of the Nebulis Sovereignty, but when her sister Elletear gets wind of her relationship with Iska, her birthright is thrown into jeopardy! Meanwhile, her other sister Sisbell is acting strangely, and unbeknownst to Alice, she's planning to track Iska down herself...