In "Undertale", The SOUL is the very essence of one's being, whether one is human or monster. In the game, a human soul and monster soul together can cross the barrier, while seven human SOULs are needed to shatter it entirely.
A soul takes on the form of a heart, human souls come in several colors and are stronger than monsters' souls, for this reason, human souls persist after death, since Determination resides in a human's soul.
Powers and Stats
Tier: Unknown | 2-C
Name: Human SOULs, Unknown individual name
Classification: Culmination of One's Being
Attack Potency: Unknown (While Human SOULs have been described as extremely powerful, even matching all the monsters' SOULs, not all SOULs reach their fullest potential as Frisk did.) | Likely Multi-Universe level (Allowed Flowey to achieve this level of power, also managing to strip him of said power after freeing themselves.)
Speed: Likely inapplicable (SOULs merely grant the powers to the user instead of functioning as actual weapons)
Durability: Likely the durability of the user
Weaknesses: The SOULs can, if they decide to, turn against the user, typically if the user is considered evil
Prerequisites: Being a monster or have them want to help you. Although not needed for use, one needs to be strong enough to completely control these SOULs. Someone with a single SOULs will have the control of their body split between them and the SOUL, while someone with 6 SOULs will possess much stronger control, but will still loses them if someone with enough determination calls out to them. 7 SOULs or higher seems to grants perfect control, although this is just speculation.
Notable Attacks/Techniques: Light Blue SOUL (Patience), Orange SOUL (Bravery), Blue SOUL (Integrity), Purple SOUL (Perseverance), Green SOUL (Kindness), and Yellow SOUL (Justice)
Key: Individually | 6 of them