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A harem includes three or more characters who potentially show romantic interest in a male protagonist. The sex, gender, or orientation of the harem members is irrelevant as long as they exclusively, or at least primarily, are vying for the affections of the same individual - who may or may not reciprocate towards one, several, or none of these romantic rivals.

Horror anime create an atmosphere of unease. Like Mystery anime, they encourage viewers to learn more about their world... but there may be secrets that are better left unexplored. Through eerie music and sounds, visceral or disturbing imagery, or startling moments, works of Horror make you worry about what gruesome thing is coming next.

Mecha are self-propelling machines that are modeled after humans; some can change into multiple, non-humanoid formats as well. They're usually controlled by an internal pilot or by remote, but are sometimes sentient beings that move autonomously. A mecha's size ranges from bulky, wearable armor to a massive, towering contraption and beyond. While mecha have a wide range of applications, such as making manual labor easier, they are most commonly portrayed as heavily-armed war machines.