User blog comment:Jopjopjop/SlashDog/@comment-3965848-20190115140610/@comment-10330822-20190116012234

Striker's right, Chisato's first cousin was just Basara's surrogate, the actual egg came from Sapphire, Mio's aunt. The actual fetus was removed from the biological mother and placed in Chisato's cousin. So there is no direct blood relation between Chisato and Basara.

Basara and Mio are first cousins, which isn't all that odd in Japan, and definitely not all the odd when it comes to royalty. And honestly, even if Chisato was related to him, she'd been his first cousin-once-removed, which is less strange that a first cousin.