Tsukune is later injected with Moka's vampire blood and undergoes several major bodily changes, emerging as a human/ghoul hybrid and possessing semi-vampiric powers.
Tsukune's normal appearance is that of a human. However, due to several consecutive blood injections by Moka, Tsukune's body began to change. His body is in constant pain, and if injected one more time he would most likely die. During his confrontation with the Outcast Ayashi, Tsukune was pushed to his limits and forced Moka to once again inject him with her blood despite the dire consequences. Tsukune fortunately survived the injection but with a unforeseen side effect: Tsukune lost complete control of his vampire blood, driven only by the base instinct of the vampire - violence and blood. Moka saw that the only way to stop Tsukune was to kill him, but just as she was about to, the head master and Ruby arrived on the scene and sealed Tsukune's blood bringing him back to normal.
Despite having the holy lock to seal away the blood, Tsukune was still not completely back to normal, he began thirsting for blood and was still able to summon up his vampire strength. Tsukune was able to suppress his blood thirst by sheer will of not wanting to hurt anyone close to him. The lock unfortunately was not originally made for Tsukune, so it was not 100% effective, if he overuses his abilities it will slowly begin to crack away at the seal, and if the lock is completely broken he can ultimately lose his life.
Tsukune is a gentle person. Although there have been many instances where he has been put into dangerous, life-threatening situations, he has never held a grudge against anyone. Tsukune's selflessness and courage come to the foreground whenever he or someone from his group of friends is faced with the possibility of injury, or even death. This ultimately led to him gaining the affection of Kurumu, Mizore, Ruby and Yukari.
As Tsukune's opponents become more and more powerful, Tsukune eventually opts to train to become more adept at controlling his powers. With the assistance of Ruby and Moka, Tsukune was able to focus his yoki and control his vampire abilities to much greater extent than before. All of this for the sake of not wanting to see Moka and his friends in danger anymore.
During the Memory Arc, Tsukune found out that Outer Moka is a fake personality and is unable to cope with it; leading him to become severely depressed and trapped within the seal. However after seeing one of Moka's memory after she was sealed, he confessed that he understood that the pain and depression she went and also said that he went through the same feeling. Tsukune said ever since he met her he felt very happy and it was the best thing that ever happened.
Tsukune's infatuation with the kind-hearted Moka often results in him letting his guard down, long enough for her to bite him on the neck and ingest his blood. While it saps him of energy for nearly the rest of the school day during the first few times, after subsequent times, it feels like more of a playful, affectionate gesture from her (in the anime, this is personified to the viewer as a kiss). Occasionally, this results in many girls on campus falling madly in love with him, while the male student body holds contempt against him. A running gag in both the manga and the anime is whenever Tsukune and Moka are about to kiss, Moka would always end up biting his neck and sucking his blood, instead of actually kissing him. There are times, however, when Moka really wanted Tsukune to kiss her, but often, those tender moments are interrupted by Kurumu Kurono, Mizore Shirayuki, andYukari Sendo. Tsukune has also showed slight perversion, such as in season 2 episode 5 when he was thinking about Moka cooking, he had a fantasy of Moka wearing only an apron when offering him a table of her food. However, due to the anime being vastly different from the manga, this may not be canonical. The manga, however, shows him having a dream of sleeping with Inner Moka, which he can't believe he had himself.
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