After Dying, I Reincarnated As The Magic Crystal of Demon Lord

Karo means diamond, after dying from a massive train crash, Karo reincarnated. But, instead of being reincarnated as a human being, she reincarnated as a magic crytal necklace of an elf. But, unfortunately, the owner died during expedition in dungeon, hundreds of years passed, again, again, then Karo picked up by a merchant and been sold as an accessory. She met the young demon lord and attracted only that child with her magic because that demon lord was the one she admired in the book from her past life. She saved him while been attacked by mid-level monsters and exhausted her mana. Now, she only an almost magicless crystal necklace worn by demon lord (Maou-sama). She believed that this will be the last one. “Maou-sama, I will protect you well. So, please don't leave me alone.” It is a two leading, female (the spirit of magic crystal, Karo) and male (the hero, Rico). Both wanted tobe saved, but ended up as the one who needed to save. One got reincarnated, the other got summoned. There was Lili who died from being shot by her ex and ended up hating male. She was ashamed of hating others who might be caring for her. The hero she met in previous period was the reason she come to being neutral. And here come the hero that caught her attention once again after the last that perished more than thousands of years ago. Should she help, the hero who wounded mentally and searching for a way to return? “You may come to hate me… and heroes would end without either love or fear, then you still want tobe a hero?” Also, a school where they all gathered would be a new way of adventure for them. >>Please tell me if there were any mistake in my grammars or another ＆ hope you enjoy the story~