\ˈhir-(ˌ)ō ˈsin-ˌdrōm\ (noun)
1. An infrequent, but nonetheless lethal,
psychological occurrence in a male character from any of a variety of TV media, particularly those found in
Japanese anime, in which the character in question experiences a drastic and negative change in
personality due to the on-comings of a female character, or in order to gain a female character's interest or attention. This sudden change in behavior can lead to a falling-out with any number of friends, peers, or companions; resignation from or disinterest in a formerly favored career track; moodiness or downright cruelty; and, in general, the taking of sudden and drastic actions that may work as a plot device but are otherwise completely out of line. While these alterations in a character's attitude are usually temporary, they can, on instance, ruin a character forever. If the character in question is a "fan favorite," then his sudden change
for the worse is all the more upsetting to any dedicated fan. The term originates with the character Nakano "Hiro" Hiroshi of the anime Gravitation, and how in his romantic pursuit of the character Usami Ayaka, he turns into what many fans consider a complete and utter douche, and takes his unrequited feelings out on his bandmates and friends.
2. When a male anime character previously assumed as homosexual abandons all prospects of a
relationship with a male because of the influence of a nearby female, enormously disappointing the avid BL fan.
