Note the above two shots - they look different, but Riku is the light source in both. I also believe that the "mirroring" going on is symbolically intended, to represent an "alternate reality".
The night of the storm has some visual parallels with the KH1 opening so that's why I've included it. I would've added more but image limit.
Why did they choose this visual parallel?
From https://www.khinsider.com/forums/index.php?threads/kingdom-hearts-3-ultimania-scenario-mysteries-interview-translated.219167/
Riku is there on behalf of Repliku, whose altered memories had lead him to believe that the promise Real Thing exchanged on the night of the meteor shower was with Namine, while in reality it must've been Sora.
The significance of Riku's "presenting" gesture is still a mystery, but my speculation is that it has something to do with the meteor shower promise, probably to take Sora's hand, symbolizing their heart's connection, and also the making of the promise.
It's meaningful that the hands of Riku and Namine actually touch, symbolizing a connection and the fulfillment of a promise, while Sora tries but fails to reach Riku's hand, both on the night of the storm and in the KH1 opening. Riku and Namine's hands are set to a bright sunny day, while Sora and Riku's are set to a stormy night (or underwater in the opening). So the situation between Sora and Riku has yet to be resolved.
---Even though Riku was the rightful owner of the Keyblade, then why did Sora obtain the Keyblade in the beginning?
Nomura: Even though I would like to keep that obscure, there is a scene in Destiny islands where Riku is being swallowed by darkness, a light appears, and Sora first obtains the keyblade. With the setting I created, the darkness that surrounds them is Riku’s heart’s darkness. At that moment, Sora enters the darkness, and the light he sees inside is Riku’s heart’s light. Sora, who was squirming in the darkness to save Riku, touched the light and temporarily obtained the Keyblade from Riku.
From the KH1 Ultimania, https://kh-ultimania.livejournal.com/3508.html
Many times we see memories depicted as light, so I wonder if in this moment, this light in Riku's heart, is actually the memory of the meteor shower promise, and in respecting it, the keyblade is bequeathed to Sora in order to protect him.
Also note that we can see both of Sora and Riku's signature colors, red/gold and blue/silver.
