After he returned to the Dark Kingdom, Kunzite knew he would be in for it. Queen Beryl saw everything. She would know that he had found out the civilian identity of a Senshi and kept it from her, that he had intended to use her to gain the key but instead fell in love with her and let her destroy it. And she would be angry. She would have some horrible punishments in store for him. And she did.
"Kunzite." Her voice dragged slowly and painfully, like liquid metal. "You have betrayed our cause. You know that in any normal circumstance, this would warrant you death. But you are no normal circumstance. You are too valuable to throw away." The coldness of her voice chilled his blood and turned his bones to ice. It gave the impression that he really could be thrown away, if the urge took her. "Therefore, I have decided to enforce upon you the harshest punishment possible without permanently harming you. I know you will not divulge the identity of Sailor Venus willingly. And I also know you have come to believe the illusion that is love, and that you think yourself in love with Sailor Venus, of all possible people. Therefore, I shall erase from your memory the very existence of Sailor Venus, and any phantom emotions you have fooled yourself into feeling for her."
Kunzite's heart sank and his body wished with every fibre to rebel, to stop Beryl taking his memories of love. The light, the purity he experienced with Venus had been such a release from the darkness that was all he'd ever known. He prayed that his Queen would reconsider. He prayed that he would be allowed to remember the love he had felt. Being with Venus meant everything now. The darkness held no further comfort for him. His reverie broke when Queen Beryl spoke again.
"I shall inject you with a further dose of dark power also, so that you will not succumb to this weakness again."
Kunzite resigned himself to his fate. He knew that urging his queen to reconsider would only tempt her to kill him, and Venus as well. It may have been the better option, but he realised that his love for Venus was not in himself, but in her. He knew now that no matter what happened to him, all he truly wanted was her to be happy. Fighting back would only bring the wrath of the Dark Kingdom on her faster. This was the best path to take. It tore him apart, but he knew he had no choice.
As Beryl's guards took him to his fate, he realised something else, also. This path, this room was familiar. As they laid him the cell, reminiscent of a ribcage, and locked him in place, he felt like he'd seen this before. And as his queen began to draw energy from some mysterious source, something that, through the haze of his consciousness, sounded like Metallia, and as it engulfed him, he realised that he had felt this before. This was not the first time the queen had taken his memory. He had been subjected to this once before. In the distant past, after the battle of the Moon Kingdom. He had almost thrown in the fight to save Princess Venus. And then the pain started. As the dark energy flowed through him, he instinctively tried to salvage memories of his love, of her, of the kisses and the closeness and the emotions and the everything. But the harder he tried to holder, the easier the darkness pulled it away. And within mere minutes, he rose again.
But he rose differently. He rose as a loyal soldier to the Dark Kingdom, with no memory of his love of his lover, nor any memory of love itself. He rose evil, through and through. He knelt beside his queen. "Queen Beryl-sama. I swear anew my commitment to my cause as a soldier of you Dark Kingdom." He knew not why he said it, for he had done nothing to cause her to expect him to break his first oath. He knew only that he must crush anything in his path so his queen could rule unquestioned.