Organs

The brain always sleeps in its room at night.

Heart - sweet, kind, caring. Emotional and wise.
Right Lung and Left Lung are a bit shy and only speak when asked.
Liver is grumpy, but sometimes kind. Caring, despite his grumpiness, he loves his organs.
Stomach is sweet and likes to be friends with everyone. He loves food, especially fruit salad. :3
Spleen - gives orders to leukocytes, a little formidable.
Right Kidney and Left Kidney - playful, toxic, sometimes a little rude.
The intestines are silent and calm.
Brain is smart, calm, and modest. He often irritated the Doctor with his intelligence, so the Doctor made him dumb :_ (theory)
The doctor is ruthless, but also somewhat kind. He's an energetic showman and incredibly artistic.

All the organs are humanized and drawn. The doctor, too :P

The doctor isn't afraid of anything (or even worried) and always maintains energy, cheerfulness, and a sense of artistry. He rescues organs in dangerous/critical situations. He sometimes likes to joke about them.
In general, he almost never worries, even if something seems strange to him. And when his organs cry or are scared, he doesn't worry. He constantly interacts with them tactilely >:) He also has keys to all the rooms.
The Doctor can hover, levitate, and fly. Essentially, they're all the same thing.
Even though the Doctor is ruthless, if he's done something wrong, he always (by any means necessary) takes great pity on the organ he's wronged, so that they don't leave the show. And he doesn't do this out of fear, but rather... simply.
The doctor always helps the organs and treats them when they are sick or in danger.

The organs love to chat :) Usually, they spend time in the common room (a regular space with white walls/floor, where the Doctor tells them something).
Fact: Some authorities sometimes call the Brain crazy because of the dangerous adventures he arranges (but it’s not his fault :<).