Veldora had always been more than a bit socially inept and inquisitive, and that hadn't really changed after all these years. This time however, that tendency certainly was a lucky break for Guy. Veldora had transported himself through space to investigate a mysterious aura that he felt, although he was delayed a bit due to his negotiations with Ramiris.
Quite a few years ago, Ramiris had regained her former form, and decided to stay in the labyrinth permanently. With her newfound maturity, the one thing she was scared of more than anything is reverting back to her previous ditzy self. Reasnobly enough, she didn't want the source of the labyrinth's magicules to leave. Only after Veldora reminded her of his [Parallel Existence] and promised he would come back immediately if it was unsafe did she agree to let him leave. Veldora would have left by himself, but Ramiris had sealed the labyrinth off from unwelcome spatial transfers due to her paranoia.
While the aura surrounding the presence was incomparable to what he remembered, Veldora could still see someone who looked just like Rimuru at the center of it with his [Chaos King Nyarlathotep]. Overcome with an incomparable happiness, he cheerfully greeted Rimuru with no hesitation.
Surprised at the interruption, Rimuru turned his head towards the newcomer. The man had spiky blond hair with a masculine appearance, yet his facial features were identical to Rimuru's own. Moreover, he felt an inexplicable tug towards this man, his very soul was reacting to their close proximity. Intrigued, Rimuru revised his original assumption that himself and the person the book talked about were separate individuals. Too many things out of the ordinary had happened to be a set of coincidences.
There was only one logical explanation for this connection Rimuru felt, in his mind. It had to be his only family member, the storm dragon who named him. To confirm his thoughts, he simply said "And you're Veldora, I presume." Veldora chuckled, still unaware of the situation, and retorted "What do you mean, I presume? Of course it's me, how could you forget? That would be impossible for one as good-looking as I!"
Rimuru reacted to those words as if he had been struck by lightning. He started muttering to himself "how could I forget" over and over again as his eyes glazed over. His aura started fluctuating from mildly oppressive to overwhelmingly harsh. Veldora, wracked with agony, moaned. "Stop releasing your aura, you're the one who taught me to keep it contained for the safety of others." It had finally occurred to Veldora that something had changed within his little brother.
Rimuru had just realized that for this world to be his birthplace, he must have forgotten everything about his life. This contradicted his belief that he had maintained for eons, the belief that he was the perfect being. His brain was quite literally being torn in half.
In response to the dichotomy, he intensely pondered the irreconcilable evidence for both sides, and waffled between the two. The mental warfare between each possibility was intense enough to spread its influence into the physical realm through Rimuru's aura.
An instant after Veldora's plea, Rimuru came to his conclusion, one that would satisfy the quandary. Either he must regain his memories of this place and maintain them, which would also require him to know how he lost his memories in the first place, or he could simply erase this universe. To him, there would be no harm in lacking memories of a place that didn't exist.
And Rimuru was perfectly content with the option that he knew he could do easily.