Serika is a member of the Kurusugawa family, which is quite wealthy and operates a conglomerate of companies in their name, including the labs which produced Multi and Serio. She speaks very quietly and it is very difficult to hear what she says unless standing right beside her - as a result, we often see Hiroyuki repeat what she just said.
She is addressed as "ojou-sama" (a very respectful title) by the family servants and is picked up by a limousine everyday. Serika is also very much into the occult and is the sole member of the school's Occult Research Club. She is also often protected by her butler, Sebastian, which has become the source of comedy in many dojinshi.
In To Heart: Remember My Memories, she demonstrates the level of authority she has over the Kurusugawa group by overruling the security of a Kurusugawa-owned Amusement Park when Hiroyuki and company try to break into it at night.