Tensura: Unbecoming

This story takes place during and mere moments after Rimuru Tempest' evolution into a Awakened Demon Lord. During this Evolution, due to the Presence of Storm Dragon Veldora, the newly acquired Raphael manages to analyze Veldora's core and leaking magicules and upgrade Rimuru into a True Dragon, becoming the fifth one in existence. See how is attitude and journey throughout the world is affected by his significantly more powerful presence.

(Keep in mind, this story will have a completely different route with the similar events, just not taking place as they originally did, but cosmology would be vastly different and attempted to be explained in better detail plus a whole bunch of differences.)