Long before the events of Rosario + Vampire, there was a very powerful vampire named Shinso. Those who inherit his power by absorbing his blood are given the title of "Shinso". Alucard the oldest existing vampire who also held the title of Shinso tried to take over the world, leaving fire on the entire continent for seven days. Another Shinso and her two companions stopped Alucard. The three who stopped Alucard later were given the title "Three Great Dark Lords". To this day, the corpse of Alucard is being watched over by the Three Dark Lords and the Shinso that sealed away Alucard: Akasha Bloodriver. Ever since Alucard's defeat, his body has been kept in hiding never to be seen again and the title and identity of the second Shinso seems to be kept a close secret for her safety and to prevent the birth of another Shinso like Alucard. In Chapter 32 Season 2, it appears Alucard is awakened when Moka awakened her Shinso power. Currently the only Shinso alive is Moka Akashiya. Tsukune Aono has also been injected with Shinso blood, but he could only transform into a vampire temporarily, however after becoming a modified-human he show's better control over his Shinso blood.
It has been shown that Shinso vampires possess a terrifying and immense aura that is darker than the darkness itself along with showing that Shinso vampires also possess incredible speed and strength on a level much greater than S-class vampires.
Shinso vampires are also shown to have immense healing abilities, beyond that shown by other vampires. Akasha Bloodriver was able to heal after being cut in half at the waist by Akua Shuzen.