Sei is Kebu's twin brother, and is a member of his class. Sei has power over cerebral chemistry, she can “absorb” the anxiety of others and then emit the negative energy as psychic energy bursts. She lies to her brother and peers by telling them that she can absorb their anxieties without any negative repercussions, but in reality, she becomes more anxious herself the more “anxiety” she absorbs

Hence, she is chronically anxious, but is in denial about her condition.