@gregger
He has 'corrupted vitality', aka so much vitality that any human or regular succubi would eventually die from having sex with him, the doctor said that only a Succubus Queen can handle him. Nono is a relative of the queen (or the queen herself?) so she can handle him alright.
This chapter just shows that if Yuuki releases his vitality he can overwhelm others, even succubi. Note that he was even reluctant to touch Nono before she reassured him so it seems that just touching others can have an effect.