Tsukune's Holy Reiki Lock
Rosario+Vampire Alternate Universe
Descended from Monster Hunters
Tsukune is descended from a long line of monster hunters. They particularly specialized in fighting renegade and bloodthirsty Youkai, they were trying to break the power of the Youkai and provide a better future for humanity from the shadows of society. The secret to their success is that over the centuries, his ancestors developed the inhuman ability to create, channel, and use youki to fight and enhance their bodies/attacks with, despite not being Youkai themselves. Some of them possessed youki so powerful that they could easily be considered S-class youkai themselves, but they needed to train extensively and harshly to attain that power. This is an ability that is only present in his direct family's bloodline.
However, use of the youki comes at a tremendous risk. Because they are humans, they are not naturally compatible with using youki. The youki strains their bodies very quickly, breaking tendons, tearing muscles, and splintering bones. If left unattended, the accumulated damage will cause them to collapse in the midst of battle, killing them flatout if they're not careful. But another problem is that the youki amplifies their fighting instincts just as much as their abilities. They must use their own human spirit energy (reiki) to shield their minds, which is a tremendous strain on them on top of the damage they sustain. If the youki overpowers their reiki and takes over their minds, they go into a berserk killing spree that only stops when they're killed or incapacitated. This is why the youki is used only as a last resort if defeat and/or death is inevitable.
Thankfully, they learned a way of restraining and containing their powerful youki behind special charms. Interestingly, the charms can also protect their minds from certain youki-based psychic attacks, like telepathy or the succubus Allure. These special charm locks allow them to utilize their youki as a true last resort surprise attack, allowing them to deliver a fatal killing blow and quickly reattach the charm lock.
In the tradition of his mother's family, Tsukune received special training from an early age in mixed martial arts and weaponry. Sadly, his skills (unlike the rest of his family) never rose above average because he didn't feel there was a need for having such things. After all, monsters and youkai had been long since exterminated by his ancestors. But where he was lacking as a fighter, his skills as an acrobat were nothing short of superb since he was an avid free-runner and parkour was his favorite hobby, something his mother actively encouraged him to partake in.
Due his ancestors efforts, the threat of monsters destroying humanity has become somewhat lessened, along with the decline of recent monster populations, and thus Tsukune's parents are relatively normal in comparison, with the exception of needing their charm locks. Tsukune grew up with monster-hunting bedtime stories from his mother and her parents. To him, the stories are just stories with only his need for the charm lock to prove there was some validity to them. But all that changes when his father unintentionally sends him to Youkai Academy and he realizes that the threat of monsters is still very much present and alive. He realizes that the monsters weren't necessarily dying out, but that they'd also gotten smarter in how they'd hidden themselves.
Because of his family's long history of being monster hunters, he is highly hesitant to make any friends while he's at Youkai Academy, which ironically only increases his girl friends' desires to become his friend once they realize just how different he is compared to the other boys of the school (I'm not talking about him being human either).
I think a good base power level for Tsukune at the start of story should be a low D-class. And of course, once he realizes that the threat of the monsters and his potential for immenient death pushes him to take heightened levels of martial arts and reiki/youki training to boost his power to help him defend himself and his friends.
There are a number of other ideas for drama. Like Moka realizing that he's descended from a long line of monster hunters due to them being one of the few humans who were ever able to actively hunt and kill ancient vampires. Tsukune trying not to introduce his friends (monsters) to his family (monster hunters). Tsukune kicking Kuyu's ass after his charm lock gets forcefully removed. Tsukune not needing to get blood transfusions from Moka to be powerful.
The pairing can be whatever you want it to be. Though I normally dislike it, I confess to this series being best done as a harem or multiple pairing for Tsukune. But if I had to choose one girl, I'd pick Kurumu every single time.