Kanna's Circumstances from Cross Make 2009, written by Moonzero (Lim Dall Young) and drawn by Anicd, is a hentai doujinshi story created by the originator of Unbalance Unbalance. It is a non-canon official doujinshi story set in the Unbalance x2 universe. It is part of the Lim Dall Young World. It is based on the Japanese version of Unbalance X2.
Kanna (Shirohime) meets Setsuna in an empty room at their highschool where she is posing as his teacher Shirayuki-sensei. She, still being affected by a magical attack, is attracted to him. He orders her to strip, and starts to fondle her, and she is mentally unable to reject the advances. He starts molesting her with a giant dildo made of oni (demon) eggs. The eggs end up stuck inside, and she has to "lay eggs". After its all done, he requests that if she really loves him, she'll kill her sister Rena (Kurohime), the rival to Kanna at Setsuna's household, so that he can live out his life, instead of dying when his Bankirou Heart ripens. She complies, so that she can continue to live with him, instead of taking his heart, as she loves him.
This links to various elements in canon. Kanna does pose as a teacher at Setsuna's school. Kanna and Rena are rivals that will harvest the Bankirou Heart when it ripens, killing Setsuna. However, they are sisters who would not kill each other for it. They would rather compete for Setsuna's attentions for selecting which one of them is more deserving of it, by which one Setsuna calls for protection more often. The heart will ripen 10 years after he made the deal that got the two sisters embedded in his household. Kanna was magically poisoned, and fell in love with Setsuna in canon, but was eventually cured of most of the effects, but still seems to show affection in canon. Both Kurohime and Shirohime are great warriors, since they need to protect the heart from other oni who would steal it.