[Crossover] Why Is This Holy Grail War Full of Love Triangles?

You are an ordinary college girl. One day, you transmigrate. In your first life, you arrive in a land that worships the gods, where you serve as a devout priestess. The god's first task for you is to become the next king of Uruk's tutor: protect him, guide him, and help him become a worthy Heavenly Spear. You diligently assist him until the little blond prince ascends the throne. Just as you think you can finally retire, a sacred marriage contract descends from the heavens. “Stay by my side forever.” The young king of Uruk takes your hand. In your second life, you arrive in a land of knights, where you are an ordinary farm girl with a little magic. Though war rages across the land, you live peacefully in a remote corner, until one day you find a young woman in heavy armor unconscious outside your home. You quickly become friends. You are amazed that she joined the Knights at such a young age, while she envies your simple, peaceful life. “I have you all to thank for this!” You sincerely take her hand. The knight's cheeks flush with flustered color as you tell her how grateful and respectful you are toward the warriors. “Thank you... truly.” Leaving only those words behind, she disappears. But in the royal capital, the heartless King Arthur returns to the throne. War soon reaches your home, too. Just as you grab your bow, ready to defend it, a group of knights takes you away. “Congratulations. You've been chosen to be King Arthur's queen.” You stare in shock at your friend on the throne. “I'm sorry. I just missed you so much.” She leans forward and gently brushes your bangs aside. “Perhaps you'd prefer another version of me?” A handsome man who looks remarkably like King Arthur steps out from the shadows behind the throne. The white-haired magician who once appeared in your dreams lets out a quiet sigh. “This mistake was your doing, so you'll have to take responsibility.” In your third life, you finally return to the safe, peaceful modern world. Wait, what do you mean the world is on fire? ( . As black mud rains from the sky, you shield the red-haired boy beside you with your body. When you wake again, you have unfamiliar silver hair and scarlet eyes in the mirror. A group of beautiful maids who all look alike crowd around you. The magic worked perfectly: you're now the second daughter of the Einzbern family! You were once an ordinary college girl, and you were also a hired hand for the Counter Force. You thought this reincarnation meant you had finally quit your job for good. To free you and your older sister once and for all, you decide to do something big and start a Holy Grail War. But why are all the friends and family who should exist only in history books appearing in the present and chasing after you? And former coworkers, stop coming after me already! But none of that matters, because the Grail says it belongs to its most beloved daughter. * Second-person narration, with first- and third-person perspectives mixed in. * A universally adored protagonist: men, women, and nonhumans all fall for her. * No romantic storylines for any characters before they come of age. * The story starts in the modern era, with the past gradually revealed. * Mainly Fate, with crossovers including Katekyo Hitman Reborn! and Bungou Stray Dogs. * Lots of original worldbuilding. Please be aware that characters may be out of character. Theme: Celebrate life.