Caesium

Commonly referred to as the "nemesis" of HIMR, although (non-paradoxically) he is also referred to as his best friend. At one point he visited Daniel's mother's house. [Source: https://www.reddit.com/r/HidingInMyRoom/comments/edwuy6/caesium_continues_his_delusion_arrives_to_daniels/ ] He is also the boyfriend of Pia, who may or may not have been romantically connected to Daniel in the past.