Burst

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.

Description
In order for one to perform Burst, they will need a special item known as a Burst Heart. 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 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.