History: Back in the previous life of the Earth, Nephrite was one of Prince Endymion's generals, the second-youngest member of the Shitennou. Just like all of the generals he would have been willing to lay his life down for the prince, but one day something unexpected happened. The sorceress Beryl brainwashed the people of Earth, and everyone except Endymion was affected. As a result Nephrite went to fight against the people of the moon, led by Queen Serenity - and as he the battle reached its climax a bright light came from the tower of the Moon Palace, obliterating everyone - including Nephrite - in its path. Endymion had been killed, and the moon princess, Serenity, was unable to handle it and in an act of cold fury summoned the ginzuishou. Everyone - except those still alive in the tower (the princess, Beryl and Kunzite) were all killed. Metallia was also almost completely destroyed, as her power had been used by Beryl as a shield to keep herself (and because he was in the vicinity, Kunzite) alive. But Nephrite was most definitely dead.
Gathering up the soul stones of the Shitennou and what remained of Metallia (and after killing Kunzite, as the power had erased the effect of her brainwashing on him) Beryl returned with them to her underground grotto and waited ten thousand years, her power and Metalia's slowly returning due to the dark energy perpetually emanating from the humans on the surface. Finally, when she felt strong enough to exert her power she sent the stones back up to the surface to be reborn as humans - and, with an infusion of dark energy, to once again serve her.
Nephrite was reborn Akai Shimizu, and for the first 16 years of his life his was nothing short of unremarkable, if somewhat disadvantageous. His parents were workaholics, his teachers constantly called him out for being a slightly-below-average studen and for writing poetry in his books, and he was bullied by classmates. He became a teenaged outcast, highly emotional, and he was desperate to find a purpose for himself - especially to find someone who appreciated him, and loved him, and wouldn't hurt him. And when Beryl returned to him and invoked the spell put on his stone, Akai not only accepted her offer, he whole-heartedly embraced it and decided to abandon his human identity in favor of what he felt would be a future where he would make something of himself. He would give his all for Beryl and in time he decided he loved her more than anyone else in the world and mirrored his missions to gain her attention.
Beryl, however, was cruel and narcissistic, her desire reserved only for Endymion, the destruction of the sailor senshi and the domination of Earth. Everything else was inconsequential and her general's little crush on her did not impress. She regardless used it to her advantage, promising her favors if he succeeded, rejecting him fully if he didn't. When the senshi came and he lost to them several times, his missions became less and less frequent as Beryl utilized the other three generals - especially Jadeite - and as a result Nephrite became more and more desperate to gain Beryl's attention.
Then along came Mercury - Kunzite's brainwashed trophy from his battles with the sailor senshi, and at Kunzite's instigation she teased and taunted him for his weakness, for his failures, for his infatuation with Beryl. Finally he snapped, as Mercury and Kunzite had intended, and when he tried to attack Mercury he ultimately lost the resulting battle with Kunzite. Beryl banished him from her presence indefinitely, which benefited Kunzite as it got rid of a potential ally for Beryl or Endymion when Kunzite decided to rise up and usurp the Dark Kingdom for himself.
Not expecting anyone to see him in disgrace, Nephrite was stunned, therefore, to find Mercury coming to him, bringing him his cape, which she repaired herself after their fight. It was a surprising act of kindness that Nephrite did his best to disavow, as it was a favor from a sailor senshi. At one point he even threw it to the ground and tried to forget it existed. In the end, however, it was an act that the general would never forget - indeed it was he who defended Mercury when Kunzite tried to kill her upon her reversion, the attempt to kill her bringing back shared thoughts and feelings of rejection and comradery that the general didn't expect to feel with anyone, much less a sailor.
Meanwhile, Beryl and Kunzite were both setting in motion their own plans and schemes to further their ends; Nephrite was inevitably caught in both. On Beryl's side it was the creation of the clone and youma hybrid Mio Kuroki, her "response" to Kunzite turning Mercury who was immediately dispatched to disrupt the senshis' lives and to bring Mamoru Chiba - the Master's reincarnation - to her. On Kunzite's side it was simply to kill Mamoru as per his ambition to rid the world of the past life and gain power, which clashed with the loyalties of fellow generals Zoicite - who remembered first and sided with Mamoru - and Jadeite - who even after regaining his memories sided with Beryl.
Nephrite did not regain his memories, which merely heightened the isolation he felt in his banishment and his loyalty. So when Beryl offered him a chance to be reinstated if he followed her into battle, he jumped wholeheartedly into it, convinced Beryl would honor her promise. It would be the last promise she would break, and she would break it fully. When the battle finally started, Beryl exerted her true control over the generals, forcing them to appear and blast the senshi when they tried to interfere with her taking Mamoru. Beryl also forced the generals' swords to their throats and threatened to kill off his generals one by one if Mamoru didn't come with her - and when Princess Serenity awakened and threatened to unravel her plans with her destructive power, she made good on her promise. And it was Nephrite, the one who gave up the most to join her, who was forced to turn his sword upon himself, falling to the ground in agony. His last memory before blacking out was of Beryl smirking at him, clearly pleased at her work.
When he came to, he found he was alive in Tokyo, but human and powerless - he learned later that Beryl had made him stab himself in such a way that would have intentionally caused his soul stone to crack, if not break entirely and wipe him out of existance. In the present, however, his frustration caused him to go on a rampage of vandalism. His last victim was Motoki Furuhata, and his outbursts against him almost got him arrested. Motoki, however, took pity on him and managed to get him out of trouble, even so far as offering him a job at Crown Karaoke, the Furuhata family business. Having no other choice, Nephrite accepted the deal, nevertheless causing Motoki, who would dub the disgruntled ex-Shitennou "Nefukichi-kun", a great deal of trouble for the first few weeks.
All of that changed when he met Ami Mizuno - and instantly realized she was Mercury, who had repaired his cloak in the Dark Kingdom. At first ashamed, Nephrite began to wonder why their paths kept crossing; whenever he worked, somehow she was there. Though she sometimes had meetings with the senshi, in reality Ami had by that time remembered him and her time from the Dark Kingdom, and felt a kinship towards him. This compelled her to make cookies for him - the first gift Nephrite ever recieved from anyone. Realizing that Ami was being sincere, Nephrite decided that he would go and find a gift for Ami - and several weeks later he found them in the form of a large pair of bison horns.
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It was on his way to getting the bison horns that Nephrite's life - and the future of the Earth - changed dramatically and in ways no one could have imagined. Mamoru Chiba has absorbed Metallia into him in order to break a debilitating spell that Beryl had put on him. But Metallia was too strong, and almost immediately after he reunited with Usagi he succumbed and was overtaken. Nephrite, who was just across the street when it happened, saw the dark energy and ran over to investigate - head-long into a field that Metallia had teleported itself and Usagi to. His shock and disbelief was compounded when Kunzite, Jadeite, and even Mio appeared, only to be incinerated by Metallia's power, their soul stones shattered right before his eyes.
Running to the remains, Nephrite screamed at Metallia, only to be ignored once more; as a mere human the demon did not see him as a threat and turned its attention to the sailor senshi who had arrived, cutting them down one by one. At this, Nephrite's shock and horror turned into untold rage and indignation, especially when Metallia hit Mercury and forced her to untransform and fall. At the same time, Sailor Moon realized Mamoru had to die in order to destroy Metallia, but as she picked up his sword, Nephrite finally snapped. The next thing he knew, he had his sword in his hands, and Mamoru's bloodied, lifeless body was starting to slide off of it. Then he was knocked out by the pulse of dark energy that emanated from the dying demon's body, and he was certain the world really was ending.
Instead, he woke up in a hospital bed next to Minako Aino's, and to the admonishments on his rashness - from an uninjured Mamoru. It turned out that after Mamoru died, Princess Serenity woke up - and so did Queen Serenity, the mother of the moon princess. The queen gave the senshi the only weapon capable of killing her child - the Soul of the Senshi - and it was Ami who wielded it, killing the princess' soul and allowing Usagi to revive as she began to destroy the Dark Kingdom. With the power already summoned from the ginzuishou Usagi instead used it to heal the ruptures in the Earth caused by Metallia's influence and teleport everyone out of D Point, where the Dark Kingdom now lay in permanent ruin. The ginzuishou endured, but without the Princess' pure rage tainting her it was no longer capable of destroying the world. The tragedy of the past life had been averted - thanks in part to Nephrite and also to Ami.
Feeling real admiration and respect for Ami, Nephrite realized it was partially her who gave him a new lease on life, and he did his best to carry forth. He worked at Crown, eventually moving in with Motoki in his apartment in order to have a place to live. He changed his name back to his birth name, realizing that the Shitennou were effectively no more, even though he was once more able to summon his sword. He managed to train himself physically, because even if in the end he couldn't ever fully revive his powers he wanted to be a part of any fight that might happen in the future.
Because of this and because of the mutual connection to Mamoru, now Nephrite's only link to his past, the ex-Shitennou managed to get on with the senshi, who trained alongside him. He also helped Usagi to control the ginzuishou - which, despite not being a true threat, still managed to do things (mostly strange things and almost always affecting him somehow) when Usagi lost control of her emotions. And, most importantly of course, he saw Ami often, and in time he did get her the bison horns - and she loved them. Since then Nephrite and Ami have dated, and he dubbed her "MiMi" - his MiMi. In return, Ami is the only person Nephrite willingly allows to call him "Nefukichi-kun" (With Motoki, he has no choice), even in public.
It was on the evening of a date with Ami, a year and a half after Metallia's defeat, that Nephrite suddenly felt a tingling feeling suddenly resonate in his stomach as he walked out his door. And as he lost consciousness, he became convinced Usagi had once more lost control of the ginzuishou nearby and there was another crazy, wild ride to be had ahead...