Ririko Kagome is a bespectacled math teacher at Yokai Academy and a lamia appearing in chapter 12 of the first serialization. Seemingly innocent and deeply concerned for her students' grades, she offers private lessons to anyone willing, though at a price (according to Kurumu, Ririko tends to go overboard with her tutoring, and envies her for her large breasts). As such, she uses her abilities to drain her students' emotions in exchange for knowledge, which is done through a flower-like appendage on her tail. She also seems to have a fetish for S&amp;M outfits, claiming that it makes her male students "work harder".However, this might be only what she thinks in her warped mind.  In both the manga and anime series, Ririko tries to enslave Tsukune when he is forced to have tutoring by her in order to correct his failing grades in math, and believes that Moka is in the way of his studies (she caught Moka trying to suck Tsukune's blood, but misinterpreted it). But when Moka attempts to rescue him, Tsukune snaps out of Ririko's control long enough to remove Moka's rosario, leading to her defeat by Moka's vampire form (she was given a two-week suspension according to Tsukune, meaning she will be allowed to return to work, unlike Ishigami).  She reappears later in chapter 19, apparently not holding a grudge, to warn Tsukune and Moka about Okuto Kotsubo. While she no longer bears a grudge against Moka in the manga, her grudge against her remains in the anime, shown when she attempted to take Moka hostage only to be stopped by Nekonome in a catwoman costume. Also, her anime incarnation is slightly more perverse than her manga counterpart. It is important to note that unlike other antagonists, she is not inherently evil, but rather very passionate about the education of the academy's students as well as the status between teachers and students. 

By a bizzare coincidence, Tsukune Aono has accidentally gotten himself admitted to a youkai academy, a school attended by monsters. Just when he thinks he'll run away from there, he meets the beautiful girl Moka and his mood turns ultra happy. However, she transforms into her true form when the rosary on her chest is taken off, she's a super vampire!

Average human teenage boy Tsukune accidentally enrolls at a boarding school for monsters--no, not jocks and popular kids, but bona fide werewolves, witches, and unnameables out of his wildest nightmares! 
On the plus side, all the girls have a monster crush on him. On the negative side, all the boys are so jealous they want to kill him! And so do the girls he spurns because he only has eyes for one of them--the far-from-average vampire Moka. 
On the plus side, Moka only has glowing red eyes for Tsukune. On the O-negative side, she also has a burning, unquenchable thirst for his blood...
 
(Source: Viz Media)

A year has passed since Tsukune was sent to the Youkai academy. Tsukune has gotten used to life there, or so he thought. As a second year, him and the girls are looked up to by the juniors. On the first day back to school, a sudden encounter with Shuzen Kokoa, takes a turn for the worst. What Adventures or should we say, misadventures await our human, vampire and friends?

All-around average student Tsukune can't get accepted to any high school save one...but on his first day, he finds the rest of the student body doesn't appear average in the least. Best of all, the cutest girl on campus can't wait to fling her arms around his neck! Wait a sec'--are those her teeth around his neck too...? Tsukune's going to have one heck of a hickey when he gets home from Monster High! But does he have a chance in H-E-double-hockey-sticks of raising his grades at a school where the turf war isn't between the jocks and the nerds but the vampires and the werewolves?
 
(Source: Viz Media)