Riku uses this form by absorbing the suns extreme solar heat and energy. This was first seen on Thriller Bark when was enraged at the Mysterious Five for taking the sun from people. He ate the small sun ray peaking through and absorbed it through his body. After the time skip he can use this by absorbing the sun through his body. This form increases his speed and power exponentially. Like Burnout Mode he grows scales under his eyes and on his forearms do deal more damaging attacks. After the Timeskip he can turn his body into pure plasma to turn into a Logia for short periods of time.
Fire Dragons Shining Roar (火竜の咆哮,Karyū no Kagayaku Todoroki?, literally meaning Shining Roar of the Fire Dragon)}: This is a trademark technique of Riku that is used as the first move in everyone of his fights. In this move Riku releases large beam of fire that burns everything in its path. The first thing that Riku does is that he gathers a large amount of fire in his body that later releases in few seconds. After gathering the fire he then blows big beam of fire that can burn everything in its path. Riku has shown true strength of this fruit that he is even capable of damaging Pacifista's metallic body. In both Viz Manga, and the FUNimation dub it's called Shining Roar of the Fire Dragon.
Fire Dragons Shining Fist (火竜の拳,Karyū no Kagayaku Kobushi?, literally meaning Shining Fist of the Fire Dragon): This is another trademark technique used by Riku. He first creates now golden fire around his fist(s) and by concentrating a little more the fire around his fist(s) becomes hotter and bigger. When Riku hits his opponent aside from burning the place where he hit, he also causes great physical pain on opponent's body. This move can be used with both fist's or only one, with two fist's Riku can deal multiple attacks and with only one fist he can cause greater damage. In both Viz Manga, and the FUNimation dub it's called Shining Fist of the Fire Dragon.
Fire Dragons Shining Arrow (火竜の鉤爪,Karyū no Yajirushi?, literally meaning Fire Dragon's Arrow): While in Solar Mode, Riku surrounds his entire body with the golden fire granted by the sun and then propels themselves toward the target, leaving behind a long wake of flames that takes the form of a arrow, and hitting them with a devastating headbutt. This unstoppable and destructive move was used to defeat Kruger and destroy one of Oars' shoulders. In both Viz Manga, and the FUNimation dub it's called Shining Arrow Strike of the Fire Dragon
Hi No Ha Style
Full Dragon Form
In this form Rku turns into a dragon made of pure superheated plasma. This form looking like his regular form but with no sign of a face just flames.