Real Knife is Chara's primary weapon, ranging a 99 ATK power, which may be enough to kill an opponent with a single hit. And once Chara absorbed the extracted Determination of the other humans, they gained the ability to alter their knife to accommodate the individual powers of the souls.
- 99 ATK: The knife can deal around 99 damage to its enemy, which is enough to kill any living entity.
- Red Blade: When the knife turns red, it can use a variety of attacks as listed below:
- Red Slashes: A powerful slash, it creates an explosion on impact.
- Dark Red Slashes: Same as the red ones, however, they need to be activated in order to start moving.
- Red Shield: This shield surrounds a certain area, which explodes after a few seconds or when activated.
These abilities are only valid for Season 1. Also, the following abilities appear only when Chara absorbs other souls determination.
- Orange Blade: Functions like the Red Blade, but can be moved to a certain direction before it impacts.
- Yellow Blade: This blade shoots projectiles at its enemy, and the attack can be charged in order for the projectile to deal more damage, the size of the projectile increases as well when charged.
- Green Blade: Wherever this blade is slashed a powerful green shield will spawn.
- Light Blue Blade: A sticky string comes out of the blade and attaches itself to its enemy, it can be cut off to be detached. When the string is pulled by the blade it cuts through their enemy like a sword.
- Blue Blade: The blade of the knife disappears and is replaced with an energy blade instead. The length of the blade can be controlled by Chara. It is slightly more stronger than the Red Slash.
- Purple Blade: It sends a triple-slash attack that will always pass through one attack and will explode on the next thing it crashes against.
- Black blade: This blade creates an orb of HATE that Chara sends towards their enemies.
- Frisk originally possessed the same weapon, without the ability to create different colored attacks in their Genocide Run.
- The different colored attacks can only be triggered when Chara absorbs the other souls' Determination.
- Chara has this knife when they replace Frisk in Season 2. The knife, however, is fully red.