The Moon (月 Tsuki in Japanese) is a noteworthy part of the Soul Eater world.
Obviously, the Moon is in the sky, and only appears at night, but the strangest thing is that sometimes, the clouds pass behind the Moon, which gives the impression that it is actually inside the atmosphere.
Occasionally, the Moon also makes an appearance in peoples' minds or hallucinations.
A giant bright and yellow moon, no matter what the time, the Moon is always in a crescent shape. It appears like a face looking to the side, with a long curved pointed nose and an ever-present large toothy grin. A single large crater with a big googly eyeball seen in the darkness of the crater serves as its eye. In the anime, it is almost always snickering to itself. At some parts of the series, blood comes out from its mouth.
Whilst appearing in people's minds or hallucinations, the Moon's appearance takes on a more gruesome look. In Masamune Nakatsukasa's soul, the Moon is black, constantly pouring a heavy stream of black liquid from its mouth. In the anime, a Moon also appears in Stein's mind whilst he is suffering from madness. Here, the Moon is a deep reddish pink, with an angry face and red eyes.
Part in the Story and Symbolism
|“||Is everyone doing their best?||”|
—The Moon, Chapter 12
Although it does not have a clear personality, Ohkubo occasionally gives both the moon as well as the Sun some 'dialogue' (although this is unclear). Usually, the Moon's dialogue is often associated with sarcasm and dark humor. Its twisted appearance is somewhat more frightening than the Sun. As most dark scenes in the manga take place at night, the Moon is often symbolic in representing the antagonists of the series and their various schemes and doings. It also drools blood at scenes of carnage and bloodshed, (it is a rumor that it drools blood when blood is shed in its presence) giving it the theme of death and murder. It is seen as the negative to the Sun's positive energy.
It can also be seen as a symbol of the madness present in the series. It is often there when insanity is in the air, looking insane itself along with some of the characters. This maybe a reference to old folklore, how people believed that the moon is what causes insanity, hence the terms lunacy and lunatic. In the Manga, this was later proven when Maka discovered that the Moon was where the Kishin Asura was hiding throughout the whole series. Justin Law has also appeared on the moon after Maka discovered the location of his "God" showing that somehow there is a way to survive on the moon. How this is possible is unknown, but the fact that the Kishin is on the Moon may have something to do with it since its madness has been greatly effecting both its appearance and most likely its inner and outer structure thus explaining how Justin is breathing. It's also possible that the moon actually is in the atmosphere, as mentioned before in regards to the clouds passing behind it, and how Shibusen could reach it simply with a Blimp. Also the fact that Azuza's shots could easily reach the moon with enough speed and momentum to cause damage to the kishin with full strenght. The moon also appeared even more sentient when Crona flew into the moon's nose, it sneezed, and it also showed expressions reacting to large damage done on itself. Crona uses the moons loss of teeth as a simile by saying just like the moons teeth aren't lined up, the resonance link between meister and weapon are not when infected with his/her feelings, leaving them unable to match soul wavelengths.
When Crona sacrificed theirself, sealing/dissolving the kishin from inside out with their mad blood, augmented by the Brew, the whole moon was caught within its radius, becoming the vision of a pitch-black fullmoon with its eye still visible from the bloods slightly translucent surface. It's unknown whether or not the effects of Mad Blood are permanent, but its known that Crona's Mad Blood simply ended the kishin's very existance as much as theirself.
Note: The above paragraph used "their" and variations of it as singular, gender-neutral terms to refer to Crona.