You and Mizuki have been really, really close. 

Your life with Mizuki was really calming. You grew up together, fought school life together, shared every bit of life in a platonic way. 

But one day, she discovered something from herself...

She's a succubus-vampire hybrid!!! 

Ever since then, you two started developing into something more. Something that transcends your initial the original intention of "helping her out". 

How will the story unfold?