Heartseed

Fūsen Kazura (ふうせんかずら) aka Heartseed, is the supernatural sentient that is responsible for the body-swapping phenomenon. When Heartseed appears, he is normally in possession of Gotou Ryuusen's body, though he is not limited to possessing only Gotō as he was able to possess one of the Cultural club members without difficulty. Heartseed's mysterious powers leave the StuCS with little choice but to act as his entertainment, each time triggering a phenomenon for its members to overcome until Heartseed is satisfied.

Personality
Heartseed always talks with a slow, monotone voice as if tired. When controlling others, his movements are similarly sluggish. Despite his seemingly sadistic fascination with the Cultural Club, he always refers to them politely. He is also very secretive, only ever revealing what the club members need to know and never anything more.

Motive
A mysterious being, Heartseed claims that he wishes to be entertained. To that end, he observes the Cultural Club members of the Yamaboshi Private High School, just because he thought they are an interesting bunch. Despite the ordeals he puts the StuCS through, he always seems faintly pleased when they do overcome his phenomenons.

Appearance
Heartseed has yet to appear himself in person, and that is assuming he even has a physical form. When he controls others, the possessed person's eyes always become droopy as if tired and their pupils lose their glow.

Abilities
Heartseed is shown to be a powerful supernatural presence capable of performing many mysterious feats such as and not limited to: Heartseed also implies that the abilities he has demonstrated so far are just a sample of what he is capable of.
 * Possessing others
 * Switching people's minds
 * Manipulation of (or at least predicting) Survival Rates
 * Forcing people to give into their impulses
 * Physically and mentally revert subjects to various ages
 * Allowing Telepathic Communication amongst individuals

When in control of others, Heartseed is capable of bestowing superhuman abilities to the body. For example, despite Gotou himself being a rather unimposing individual, while Heartseed is controlling him he is able to effortless fend off attacks from Yui who is a karate expert.

Authority
During the Hito Random arc, Heartseed initiates the Body-swapping phenomenon and has himself demostrated the ability to possess the bodies of others. He can start and end the body-swapping process; however he allows the body-swapping to randomly choose the candidates amongst the group as it will be more interesting. He is also capable of letting the candidates choose who they wish to body-swap with amongst themselves, but only when he desires it. It is also implied that even though he states all phenomenons are random, he purposefully chooses to activate some at a specific time to make things more interesting.

No.2
Another mysterious factor of Heartseed is his supposed alternate persona, No.2 who seemingly acts on an agenda different from Heartseed's. No.2 initiates the phenomenon during the Kako Random arc and has not been seen since after Heartseed claims to have done away with him for causing too much trouble.

Trivia

 * Heartseed's name refers to Cardiospermum, a type of vine plant. They produce balloon sacks which contain seeds with distintly heart-like indentions.
 * In the manga adaption, Heartseed is depicted as slightly more lively than he appears in other media, even smiling on occasion.
 * A difference between Heartseed and his No.2 persona is that Heartseed refers to himself using "boku", which is a masculine pronoun, meanwhile No.2 uses "atashi", which is more feminine.