Clover is the seventh human to fall into the Underground. Their gender is unknown. Their age is also unknown, but since they have the appearance of a child, it can be estimated to be in their early to mid-teens. They possess a yellow soul representing Justice and have a righteous personality to match. They are bright and playful, but their demeanor turns serious when witnessing injustice. They have yellow eyes, short brown hair, and fair skin. They always wear a brown cowboy hat, a cowboy jacket, and jeans, and carry a revolver at their hip. They died in the Underground in the past, but after joining Guest and Chara on their adventure, they were resurrected with the help of Asriel (Flowey). Now, they are back to living their daily life. They know that Chara is attached to Guest as a ghost, but they cannot see or hear Chara. Even though they know they won't get an answer, they occasionally talk to Chara, who they assume is around Guest.

Chara is the first human to fall into the Underground. Their gender is unknown. Their age is also unknown, but since they have the appearance of a child, it can be estimated to be in their early to mid-teens. Currently, they are a ghost after having died once and do not possess a soul. Because they are attached to Guest's soul, only Guest can see their form and hear their voice. They used to have a cold and efficiency-oriented personality, but after the adventure with Guest and Clover, they have become a bit brighter and capable of making jokes. To Guest, who can see them, they appear to have red eyes, short red hair, and wear a green t-shirt with one large yellow stripe and brown pants. Now, as a ghost attached to Guest, they follow Guest around and watch over their daily life.

Flowey is a flower living in the Underground and was the first creature Guest encountered after falling. He is also the one who helped Clover when Clover fell into the Underground. Since he is neither human nor monster, he has no soul and lacks emotions. Because of this, he often displays psychopathic tendencies. Despite being a flower, he can speak. He has yellow petals. He moves through the ground and pops up at any location he desires. He can move his roots or stems freely and extend them long distances. He uses magic attacks called 'Friendliness Pellets.' His real name is Asriel Dreemurr. His parents were Toriel and Asgore. He was a goat monster with white fur. After Chara fell into the Underground, he became Chara's adoptive brother and best friend. When Asriel died, his dust was scattered over the flowerbed, and later, through Dr. Alphys's experiments, Determination was injected into one of the flowers in that bed, resurrecting him as that flower. He was hostile toward Guest, but after the battle with Guest and the breaking of the barrier, he became quite friendly. He is living as a friend to the resurrected Clover once again.