Io

Io is a moon of Jupiter, he is the innermost and third-largest of Jupiter's moons, he has the highest density of all of them, and has less water than any other object in the system.

he keeps bleeding because of his volcanoes, he has 400 of them, he is the most geologically active person in the system, his bleeding and his geologic activity is caused by tidal heating of friction generated within his interior as his interior is pulled between Jupiter and his other friends, Europa, Ganymede, and Callisto, he also has 100 mountains on his surface, some of them are taller than Mount Everest (Earth's highest mountain), unlike most moons in the system, his skin is made out of silicate rock surrounding an iron or iron sulfide core, he is colored yellow because his skin has extensive plains of sulfur and sulfur dioxide frost, he also has white and red regions of his skin.

he is always been bullied since his pre-K times, he tries to make himself more protective from this, he also loves to play games ending with ".io" (like slither.io for instance)

he has been visited by several spacecraft, such as Cassini-Huygens, New Horizons, and Juno.

interactions with Jupiter's magnetic field
Io loves to shape Jupiter's magnetic field, he can develop 400,000 volts across himself, releasing ions that give Jupiter a magnetic field more than twice the size he would otherwise have.

Description
Io sometimes gets aurorae out of sodium, oxygen, and sulfur dioxide, his volcanic plumes cause him to bleed, he is always scared of blood just like Saturn.

between 1999 and 2000, the Galileo spacecraft took images of one one his volcanoes (Tvashtar Paterae) having lava flows (lava is his blood)

Atmosphere
he has an extremely thin atmosphere mainly made out of sulfur dioxide

due to particle radiation hitting the atmosphere, he sometimes gets auroras on his atmosphere (like what Earth has)

In fiction
Io appeared in many works of fiction, examples include
 * in The Mad Moon, he has 2 native people, the moronic balloon-headed loonies and the ratlike slinkers
 * in the Red Dwarf TV show, the character Arnold Rimmer was born on Io
 * in Babylon 5, he is the home of an Earth Alliance colony, second in size only to the colony on Mars, the solar system's jumpgate is in orbit around him, there are also research colonies on his friends, Europa and Ganymede
 * in Sailor Moon, the Sailor Guardians have a castle named after him, Sailor Jupiter's castle is called the Io Castle
 * in Halo (a game made for Xbox), the United Nations Colonial Advisors on him got attacked by Frieden forces which lead to the interplanetary war, in Halo 2 however, detector stations on his surface pick up a whisper that warns of covenant vessels going to Earth vis slipspace.

Trivia

 * he is the most volcanically active object in the system