Switching it up by writing about Mamoru being a papa and talking about his past with Usagi
Mamoru caressed the golden heart in his hand affectionately, the same locket Usagi had gifted him in their past life as Princess Serenity. The last remaining piece of their past as they descended into the future. Though it held no magical powers, it didn't empower either of them nor did it help them grow, it was something precious to him. It was a memory of what brought them together, a time when they were secret lovers due to them being from different kingdoms. Usagi had risked her status as future ruler to be with him, hiding this love from her mother, to which she made a promise to him with a gift. Proof of the sincerity of Usagi's love for him, a timeless object he had held onto, even when he didn't remember her, even when they forgot their lives together. He had held onto it, protected it, shielded it, he knew it meant something. During his time with amnesia, he had hoped it would answer the questions of his past and help him remember. He had briefly given it to sailor moon to protect, feeling like it belonged to her. She was the best person to hold onto it.
In the end he had made the right decision, entrusting it to the person who had loved him most. Giving Usagi the locket had saved his life, when he forgot her, when Beryl had kidnapped him and brainwashed him, before he killed Usagi. Beryl had attempted to turn them against each other, her feelings for the prince corrupted by the darkness. So she may have him for herself. Hoping to turn the two lovers against one another. She had revealed the locket to him, baring her soul to him, the most genuine form of their love, the locket that had held them together. After touching the locket, Mamoru had been purified, saved from the control of the negaverse, returned to his old self. He would give his life again and again to keep Usagi safe, what he lacked in the ability to say his feelings in words, she showed his gestures. She was his world, the love of his life. They had faced hell and back together, only coming back stronger.
Chibiusa approached Mamoru curiously, while Usagi was at college, he had been tasked with caring for her, but had promised a family date when Usagi got home. The parents she had met when they were in middle school and college were very different people. Usagi was now in college to become a doctor, while her father studied social science. He had since decided to become a therapist, to help heal people who needed it most.
She saw that Mamoru took this locket with him everywhere, no matter where he was, keeping it close to his heart, always. She knew that Usagi was the most important woman in his life, followed by his daughter. "Papa, what's that?" she asked curiously. She knew that the locket meant something to him, she could see the look of love in his eyes. Her parents in the future had never spoken much about how they met and how their romance blossomed. There was a lot from her parents pasts that she didn't know about. Mamoru gazed at his daughter curiously, Chibiusa was future queen of the moon kingdom and a child born of his feelings for Usagi. She had many questions but not all he could answer. "That locket? You're always clinging to it, why?" she asked.
Mamoru smiled, patting his lap to which Chibiusa climbed on, he loved being able to share moments of his life with Chibiusa. So that she could learn from them when she fell in love someday too. Opening his palm to reveal the trinket, able to appreciate the golden token up close. "This locket is from when mama and papa were younger, before we ruled the silver millennium" he explained. When they were younger, naive and sharing an affair in secret, sharing stolen moments together. Knowing that if they were caught, they would be punished for the love they felt.
Chibiusa stared, she knew her great grandmother was queen before Usagi, but she didn't know much about her. She had passed away when Serenity was very young. Knowing of her parents past experiences was always so strange, knowing she didn't exist yet, let alone her parents even considering children "Before you became king and queen?" she gasped. The future sailor scouts would often say that Neo Queen Serenity was a troublemaker as a princess, she would often run away and hide so she could sneak away with Endymion. But their passionate attraction to one another led to their future marriage and ruling the kingdom together.
Mamoru nodded "This locket, this was from a time when Mama was still princess of the moon, when her mother queen serenity ruled the moon. When I was still prince of the earth, before I would become king, the papa you know. When an enemy called the negaverse attacked us, by a woman called Beryl" he explained. Usagi had loved him so much, they couldn't stand to be apart from one another, constantly terrified of the consequences of their actions. When he and Usagi were royalty, yet to inherit the title of ruler of the moon kingdom or the earth, ruling two separate kingdoms so far apart. So young and so naive, two forbidden lovers who were supposed to be enemies, but fell in love anyway. Usagi had given her the locket as proof of her love for him, so that he would never forget her. They had faced many adversities together, before and after their reincarnation, people who came between them, threatened their love and their homes. Serenity had been so heartbroken at his death at the hands of Beryl, that she killed herself out of grief. Her mother had been so heartbroken at the destruction of their kingdom and her daughters death, that she used the last of her power to reincarnate them as humans on earth. In this lifetime, the thought of living without the other was heartbreaking. They had a life together, past and present, while raising a child, that would be Chibiusa. Fate kept binding them together, reminding them of being soulmates.
Chibiusa's eyes widened, though her parents relationship was often a hot topic of conversation in the kingdom, she only knew them as rulers and her parents. The depths of their personal relationship kept private. Now learning it from him in person changed her perspective. Her father when he was younger had loved Usagi so deeply that she gave him this locket as proof of that affection. Her first and only love, the most important man in her life. She knew that Usagi loved mamoru and could be childish about that at times, jealous of other women, at times even her own daughter. Many women had tried to come between them and pursue Mamoru romantically despite having a girlfriend. But every time he rejected them in favour of her mother. Knowing that they meant to each other, she could admit it was romantic. Though she was too young to understand the kind of romantic love her parents had, she had experienced some crushes. Wondering if she would find a boy that would treat her the same way. She knew that the guardian of the golden crystal and priest of Elysian; Helios was part of her future. But she had a long way to go before that future would come to pass. Finding someone who would gift her with a special token, the way Mamoru treasured it, meant he still remembered. "Mama is special to you isn't she?" she questioned.
Mamoru smiled, his heart was full of Usagi, even when they weren't together. When Galaxia threatened the earth and stole the star seeds from all living people, before he left for university he proposed to Usagi. One day they would be married, Usagi would become his wife and eventual queen, but that day was in the far distant future. "I'll never love anyone like I do your mama, and our love will eventually create you" he smiled. If Usagi was ever upset or scared, he would comfort her until she felt safe, if she was ever in danger he would protect her with his life. He would do anything for her. Chibiusa's eyes widened, gently touching the locket, something that bound her parents together, a memory of their past and future to come. She was formed of that bond, she would continue their legacy using their guidance.
Usagi sneezed lightly, a shiver running down her back, she had a curious feeling that someone was talking about her. She had learned to follow her instincts over the years, especially when it came to her daughter. She had left Chibiusa in the care of Mamoru today while she was at college. Though Chibiusa had matured greatly since her adolescence, she was still clingy towards her parents. Usagi had become better at handling her moods and guiding her not only as a sailor scout but as a princess to be. She and Mamoru shared custody over her when they were working or busy. Chibiusa still had much to learn of the world before she would come to protect it, overcoming the trauma of her past to become a strong leader. Usagi by her side, helping her daughter grow. "I wonder what those two are up to?" she reflected.