Mako Yakumaru is disquised as a school nurse sent in to assassinate Midou Kusasbi after failing to kill Tsukune. Mako uses Moka against Tsukune and his friends byinjecting her her with a hypnotic fluid to force Moka to kill Tsukune. The tactic fails and she is forced to use a number of bystanders to Tsukune. Mako Yakumaru makes her appearance in the second season of the anime in episode 4 and designated as the actual school nurse, rather disguised as one.

(Source: Wikipedia)