Oka is the president of the school's occult club. She is completely convinced that ghosts, demons, and black magic really exist, and wants to dedicate her life to proving that these things are real.
She is an awkward girl who is regarded as 'creepy' by the majority of the school, but she is actually quite harmless, and some people even find her to be endearing, as she is quiet and thoughtful. Perhaps Senpai will think that there is something charming about her unusual nature...