Shinji Matou at Your Service

The first to make a decision was Jeanne. She decided to go and see the other world. As a Heroic Spirit, a Servant, her existence transcended world lines, so crossing over wouldn't pose any problems for her.

The remaining three, Fiore, Reika, and Laeticia, didn't rush their decisions. They utilized the limited capabilities of Mooncell to investigate the state of the parallel world, and after carefully considering their own situations, they made their final choices.

Laeticia chose to stay behind because her family and friends were all in this world, and she didn't belong to the world of mysteries. Laeticia was easily content. If Jeanne went, it was as if she had gone too, and that was enough. It was an opportunity for her to reflect on her own heart.

Reika also decided to stay because she had observed her parallel self. A "world" (not just a world line) cannot have two identical souls. If she went, the other version of herself would have to disappear or temporarily leave. She didn't want to disrupt the ideal life of her other self, so she gave up.

Of course, she didn't leave things entirely as they were. She used Mooncell's power to attach a part of her thoughts to Jack, projecting them to the ideal version of herself in the other world, hoping that this other self could meet Shinji in her stead and tell him that someone still cared about him—tell him that he had a daughter.

Reika's decision to stay also influenced Fiore's choice. Someone had to stay behind to manage things, and with Reika's wisdom, Fiore felt secure enough to take a gamble.

Fiore was the one with the highest chance of success. The Forvedge family specialized in spirit invocation, and in the field of soul studies, Fiore had advanced further than most magi. Her soul strength far surpassed ordinary humans. Moreover, after the transformations brought about by the Holy Grail War and leading the Yggdmillennia clan, she was confident in her ability to traverse parallel worlds.

As expected, the crossing was a success, and she arrived on the other side of Mooncell.

The first task after crossing wasn't to head to Earth but to seek a vessel. This world was different from her worldline—in her original world, she had a physical body to return to. Here, she and Jeanne were nothing more than wandering spirits. While they were fine in the spiritual particle world, they would soon dissipate in the real world.

Therefore, they needed suitable bodies.

Fiore had already picked a target before crossing—just like Reika, her parallel self, Fiore Forvedge, in this world. In this world, there was no Yggdmillennia clan. The reason was that in this world, Darnic had died during the Third Holy Grail War, and thus, he never continued his plans.

However, the Forvedge family's situation remained the same, gradually declining, though it still produced an outstanding talent like Fiore. Much like herself, Fiore in this world faced the same dilemma—whether to pursue freedom or the path of magecraft. Perhaps because there was no hope in the form of the Greater Grail, the Fiore of this world gave up on magecraft after reaching adulthood and, with her brother Caules' help, ran away from home.

And that's where the problems started.

After all, she was still "herself," and growing up in the same environment meant sharing the same weaknesses. Fiore had excellent decision-making skills, but she was terrible at self-care and lacked common sense, often making assumptions.

When she was at home, things were fine—there were servants, and her reliable brother Caules took care of her. But once she was on her own, all sorts of problems arose.

She had to avoid being tracked by her family while also managing daily life on her own—laundry, cooking, cleaning, all things Fiore had never done before.

One more critical point: the removal of her defective magic circuits. As long as they remained, she could not achieve her dream. However, the surgery was something she couldn't perform alone, and completing it without her family knowing was her biggest challenge.

Before she left home, she had thought everything through. But when it came time to put the plan into action, the difficulties were overwhelming.

At this moment, her savior appeared—the Fiore from another world. Although she couldn't come to Earth, she used Mooncell's power to send a message to the Fiore of this world.

Since they were the same person, she knew the best way to communicate. She got straight to the point, no beating around the bush.

"Let's make a deal. I'll solve your problems, and you'll let me borrow your body."

"If you don't agree, that's fine too. We can negotiate. I won't use your body all the time. I just need to borrow it for a while. As for the terms, how about I let you keep your magic circuits intact while also giving you the ability to walk? I'll even help you find a powerful backer who the Forvedge family wouldn't dare to cross. What do you think?"

"If that's not enough, we can keep talking. I may only control a small portion of Mooncell's power, but it's no less powerful than the Greater Grail."

The Fiore on Earth quickly compromised, as she had no other choice—the gap between them was too great. No matter where she went or what she did, the other Fiore could always find her and even help her resolve several problems. Even if the other Fiore had lied the entire time, she had no way to resist. It was better to give it a try.

After some negotiations, the two Fiores finally reached an agreement to "rent" the body of Fiore Forvedge.

From that day forward, except for necessary sleep, the body would be shared equally. One would use it while the other waited inside Mooncell until the body reached its limit and began to reject the foreign soul.

That's right, rejection. The foreign entity in question was Jeanne. Fiore was not like Laeticia, who was practically Jeanne's reincarnation. Even with spirit invocation, Fiore couldn't coexist with Jeanne for as long as Laeticia could.

And given their years of friendship, Fiore didn't want Jeanne to remain stuck inside Mooncell. Even if Jeanne didn't mind, the practical circumstances wouldn't allow it—neither version of Fiore was good at taking care of herself. Jeanne, on the other hand, was from a farming family, skilled in cooking, cleaning, and all other household chores.

Additionally, there was the matter of combat. Adjusting and adapting to her magic circuits would take time, and during that period, Fiore's combat abilities would be extremely weak. If trouble arose, Jeanne would need to provide backup.

For these reasons, Fiore didn't rush to Fuyuki. She settled in Europe first to deal with her issues before going to meet the person she wanted to see—otherwise, she might once again be told she was "not mature enough."

Her introduction to Luvia also happened during this time. The two of them even resolved a few incidents together in Finland, and Fiore finally completed the adjustments to her own body.

What happened next doesn't need much explanation. When Luvia enrolled in the Clock Tower, Fiore quietly followed her, just in time for the Mystic Eye Collection Train incident. After catching a glimpse of Shinji from afar, she had a chance encounter with the Burial Agency, which led her to Fuyuki.

She didn't go straight to Shinji, for several reasons. First, she didn't want to disrupt Ciel and Caren's plans. Second, Jeanne's sense of duty as a Ruler had kicked in, and she felt obligated to fulfill her role as an adjudicator. And third, there was a bit of pettiness involved—they had been thinking about him, yet he seemed to be surrounded by one woman after another, living a carefree life. Had he forgotten about them?

And so, things dragged on until now, at the critical moment of purifying the Greater Grail. Out of a sense of duty as an adjudicator, and due to the physical limitations of their situation, Fiore and Jeanne decided not to delay any longer. With little time remaining, they opted to go all-in.

As for the issue of Jeanne's Saint ability potentially destroying her Saint Graph, Fiore had already thought of a solution—while Jeanne's Saint Graph might collapse on Earth, they could simply pull her back to the Mooncell and repair it. Problem solved!

And so, the scene of Jeanne's crimson flames purging evil, with Shinji gazing up at the moon, came to pass.

PS: The Savior class is a special class, also known as Saver. If memory serves, there are seven of them, with the only known one so far being the Enlightened One, Buddha. You can look up what kind of presence that entails. As for the other two figures from the three major religions, it's almost certain that they are also Savers. The Yahweh mentioned earlier is simply the Jewish name for God, and since Solomon is Jewish, you can make a connection there. As for this figure's abilities, the Ten Commandments already give a good idea of what they can do. Taking it a step further, it's highly possible that the preservation of humanity's future was orchestrated by him behind the scenes—how else would the ring sent to the future have conveniently ended up in Marisbury's hands?