Raito Raito no Mi/Hikariken

Hikariken
Hikariken (光剣, Literally meaning "Light sword"), is a technique that Renji created after creating "Amaterasu".

After Renji used Amaterasu for the foirst time in battle, Renji noticed that he can fight at full power in that form this is because Renji is a swordman, he though "what's the use of heating my body if i am going to use my sword in the end" this is where he thought that he can simply use a similiar method to heat up his sword as well.

To use this technique Renji would release great amounts of light from his hands and concentrate it all in his sword, heating it up greatly.

The heated sword gaines incredible cutting power, areas that are cut with the sword are usally engulfed with flames, also using friction Renji can easily produce flames by swinging the already heated up sword with extrem speed, he usally does this to create fire based flying slash attacks.

Before the timeskip
At first Renji would have a hard time keeping the light concentrated in his sword, and using the technique would also deplete his stamina nd tire him.

After the timeskip
At this point Renji has perfected his technique, he could easily concentrate light in his sword without wasting any energy, the technique no longer affected his stamina as well, he can also swing his sword in extrem speed to produce fire from the speed of the friction, because the sword is already heated up, this is very easy for Renji to do, he uses this to preform flying slash attacks that are formed of fire which have great destructive force and can inflict great damage on opponents.