Bequeathing

The Keyblade Inheritance Ceremony, also called the Bequeathing, is a trial in which a Keyblade wielder on the level of a Master chooses a person to inherit the power to wield the Keyblade. If the Keyblade accepts the inheritor selected, that person will become able to summon their own Keyblade whenever attempted. An inheritor can also be accidentally made, if one with the right heart touches the weapon; this is how Kairi became Aqua's inheritor at Radiant Garden. The only intentional ceremony seen is performed on Riku by Terra, setting Riku's fate as a Keyblade bearer.

Procedure
A Keyblade Inheritance Ceremony may be either intentional or accidental. To pass down the Keyblade intentionally, a Keyblade master must choose a successor. All the master must do is test the strength of the one they have chosen by allowing him or her to hold their Keyblade.

The Keyblade is accidentally inherited when one of a strong heart and will makes contact with it.

Prominent Keyblade wielders that practiced both cases of the Keyblade Inheritance Ceremony are Aqua and Terra. A chosen Keyblade wielder is capable of seeing the door to the heart of a world, as Riku saw in the flashbacks in Kingdom Hearts.

Kingdom Hearts Birth by Sleep
Some time before the Mark of Mastery exam, when Terra, Ventus, and Aqua were still training together, Ventus felt down about losing to Terra in a mock battle. Terra cheered him up, performing a mock Keyblade Inheritance Ceremony in which he recited the mantra and passed his Wooden Keyblade on to Ventus.

The Keyblade Inheritance Ceremony is unintentionally performed when Aqua visits Radiant Garden and comes across a young Kairi, who was being attacked by a swarm of Floods. Kairi runs to hide behind Aqua and touches the Keyblade, which causes her to become an inheritor.

Aqua also had the intention of performing the ritual with Sora when she met him in Destiny Islands, but she noticed that Terra had already made it with Riku. Not wanting them to fight like she and Terra would, she refrained, although Sora and Riku would inevitably clash with each other several times ten years later.

The Keyblade Inheritance Ceremony is intentionally and correctly performed by Terra when he meets a young Riku on the Destiny Islands. Seeing himself through the boy, someone who would do anything to protect his friends, Terra proceeds to select Riku as his successor. Many years later, this showed that Sora was not originally the Keyblade's chosen wielder when he received it. However, due to Riku's descent into darkness in Kingdom Hearts, the Keyblade was led to choose Sora, as Ventus's heart, the heart of a Keyblade bearer, resided within him. Riku would not regain the Keyblade until one year later on his path to return to the light.