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Ryouga after combining with Zekrom
Burst (Japanese: バースト Burst) is a special technique in the Pokémon RéBURST manga that allows a human to combine with a Pokémon, gaining its powers and immunities while increasing the user's physical and defensive strengths. Those who can use Burst are known as Burst Warriors (Japanese: バースト戦士).
The concept of Burst compared to a Poké Ball
In order for one to perform Burst, they will need a special item known as a Burst Heart (Japanese: Ｂハート). The Burst Heart is a small, pocket sized jewel that actually holds a Pokémon inside of it, sealed so that its power can be used by anyone wishing to fuse with it. The Burst Heart can be compared to a Poké Ball in that it holds a Pokémon inside, but is also different due to the fact that it doesn't store a Pokémon to be released for later use. If a Burst Heart is broken, the Pokémon inside will be freed. It is not known how a Burst Heart is made, but Artificial Burst Hearts (Japanese: 人工 Ｂハート) have been created by Great Gavel.
Once Burst is activated, the user will have their physical traits increased greatly. Whatever abilities the user will get depends on the type of Pokémon used to combine; for example, a Ground-type Pokémon will make the user immune to Electric attacks. It is stated that in order to use Burst, one must go through rigorous training or else their life will be in danger if they attempt it.
It is shown that a person can actually be sent inside of their Burst Heart in order to better connect with the Pokémon inside. In Ryouga's Burst Heart, an entire field can be seen inside and a large area where his Zekrom is being held. Once he arrives to this spot, a key takes the form of a young gatekeeper boy to test him and see if he's worthy enough of seeing Zekrom. Once Ryouga passes the test, the boy turns back into his true form—a key—and allows him to see Zekrom.
It is later revealed that a Burst Heart—like the Pokémon they contain—can become stronger as they get involved in more battles. This allows the Burst itself to become stronger at the same time as the Burst Warrior. Evolution still applies to Bursts; if a Pokémon inside of a Burst Heart evolves, so does the Burst of the user.
Three Artificial Burst Hearts
A failed attempt at Burst
Compass of Light
The Compass of Light (Japanese: 光の羅針盤) is a large crystal-like object that has the ability to search out Burst Hearts. Once a Burst Heart is put inside one of its six grooves, it will emit a beam of light that will seek out any other Burst Heart in the vicinity. The more Burst Hearts that are nearby, the more beams of light will seek them out. Also, the thicker the beam is, the stronger the person that possesses the Burst Heart is.
According to Hariru, if the "six original Burst Hearts" are put inside of the grooves, then Ryouga will be able to find the person he has been searching for, Arcades. Once the Burst Hearts are inserted, the Compass begins floating and then speeds off to its destination.
The six grooves inside of the Compass of Light
The Compass of Light tracking Burst Hearts
The Compass of Light flying
Known Burst Warriors