The First Bite

Nanami is a leaf ninja with the mission of observing Orochimaru and his henchmen. After a brutal battle to defend his base from secret data-seeking agents, she is in critical condition. Without Karin's healing abilities, Nanami could die. However, things have been tense between the two since they met. At the pleading request from their mutual friend Ao, Karin hesitantly decides to help Nanami.

What will the chakra-transferring bite awaken?

If the name of the series doesn't give it away, it's sex. It awakens sex.