(This interesting idea had come across my mind) Since Ruron only happened when Kuron didn't choose to help Kou regain the memories, but what if part of his memories did regained in the long run right after Kuron starts dating Ruki. And that Kou wants Kuron back? How would Ruki react to this?
"Ah... So it would seem you finally recollected that old flame for Kuron," the eldest addressed Kou with a cold, nonchalant tone. "I was certain it would've flickered and extinguished by now. Well, you're too late, I'm afraid. Kuron and I have already voted loyalty to one another in ways you wouldn't understand. Indeed, you lost your memories, but even so I cannot shake the sensation that stirs within me each time I see or think about him. At this rate you are to give up on Kuron already—otherwise we will have quite the complication here."
After seeing for himself how Kou refused to stop thinking of the common subject of their affection, Ruki failed to stifle a stone-piercing glare at the blonde. A step closer and now he glowered down at his younger sibling, dauntless and without a shred of doubt.
"No. I told you many times, Kou. Kuron is mine—wake up and smell the roses, for pity's sake. What can you possibly do for him? You haven't shared the same joyous memories that I've gained over the years with him, you lack the same wisdom as I to guide him on the fast track to success, not to mention your two-facedness is the last thing he needs right now. Would you truly dare to add more to his already piled plate? I think not. If you care about him as you insist, then you will leave the two of us alone. That's an order, not a suggestion."
Subconsciously, the Vampire had firmly seized hold of his brother's upper arm in a crushing grip as if to deter him from the one he cherished and loved most. After realizing this, Ruki quickly released him.
"It seems I got a bit ahead of myself," he started regretfully. "My apologies, Kou. Though my point still stands. Touch what belongs to me and you will receive more than just a stern reprimanding."