As a Moon fan, as a fan of the setting, as a time traveler who traveled through time to the Matou family, and as Yustisa's closest friend, Shinji definitely has the most and most complete information about the Holy Grail. Even Amakusa Shiro, who is also a time traveler, cannot compare to him in this respect.
Based on this premise, and assuming that Amakusa Shiro's purpose has not changed, Shinji should be able to think of what Amakusa can think of.
Amakusa Shiro's current situation: he has the Greater Holy Grail but not the Lesser Holy Grail, so his combat power is relatively insufficient compared to the enemies who are huddled together for warmth. If the enemy is determined to huddle together and defend, it will obviously be very difficult for him to take back the Lesser Holy Grail and hunt enough Servants.
At this time, anyone with a little bit of common sense would consider some workarounds.
What if you don't have the Holy Grail? Make another one.
Is it possible? Yes.
The main reason why Shinji is in a hurry to kill Zouken is that Zouken intends to transform Sakura into another small Holy Grail, the "Black Holy Grail". This is the world line where Shinji lives, and the secret of the Holy Grail is only circulated among the three families.
In this world line, the method of making the Lesser Holy Grail is a semi-public secret. With the ability of Shiro Amakusa and the power of the Holy Church he is lurking in, it is not difficult for him to make one himself or steal one.
In Shinji's world, because of the uniqueness of the Holy Grail system, Zouken asked "Black Sakura" to actively kill servants and snatch souls. In this world, subspecies Holy Grail wars are rampant, and it is easy to collect servant souls. It is entirely possible to collect enough servant souls first and then connect to the Greater Holy Grail - considering Amakusa Shiro's Noble Phantasm, this is not a difficult task.
This also explains why there are only five servants (the capacity limit of the Lesser Holy Grail), why there are no sabers (the limitation of the subspecies Holy Grail War), and why the servant list shows a death status as soon as it logs in.
"Danik, that bastard, it's fine if he just wanted to steal the Greater Holy Grail, but why did he let everyone know about the ritual?"
The more Shinji explained, the angrier he got, and in the end he just started cursing.
Fiore gave him a strange look: "Why are you angry? Any of us can be angry, but you shouldn't be angry. Not only should you not be angry, you should be happy instead."
"Why?"
"Whether Amakusa Shiro prepared other Lesser Grails or not makes no difference to you. If he didn't do it, you wouldn't go to him?"
"ah-"
Fiore's words were like a wake-up call to everyone.
No matter what, Shinji will fight with Amakusa Shiro to regain Yustisa.
The other masters and servants were different. There was no need to fight for the Holy Grail that could not be activated, but if it could be activated and was just one step away from the omnipotent wish-granting machine, it was another matter. As long as there were wishes that they wanted to fulfill, they would not give up the Holy Grail, not to mention that this wish-granting machine was in the hands of a bastard who wanted to destroy the world - no one present was divided into masters and servants, and no one wanted the world to be destroyed.
Amakusa Shiro's move was tantamount to tying everyone present to Shinji's chariot. No wonder Gold muttered, "I now strongly doubt whether you and Ruler have colluded to deceive us together."
Shinji denied it outright: "How is that possible? If they were colluding, I wouldn't have told Mordred and Atalanta that. With the pursuit of the Holy Grail, our fighting power will be higher."
Jeanne also said solemnly: "I can swear to the Lord that everything I said is true. Moreover, the servants were summoned by the Holy Grail, and they should be able to feel the changes soon."
Artoria followed closely behind: "I can also testify for Jeanne. I have the experience of participating in the last Holy Grail War. I can vaguely feel that something is changing. We don't have much time left."
Soon, Mordred and Chiron, who possessed skills such as "intuition" and "mind's eye", also noticed the slight abnormality. From then on, no one doubted the truth of what Shinji and Jeanne said.
"Then there is no need to hesitate."
Achilles clenched his fists and grinned wildly.
"Attack the Sky Garden and defeat those bastards. I've been annoyed with that woman named Semiramis for a long time, and I must teach her a lesson this time. And that priest named Shirou, hmph, destroy the world? You have to ask me if I agree."
"That's right. For the sake of those beautiful children, I will never let the world end - it has nothing to do with whether I want the Holy Grail or not."
Atalanta bit her lip and said with a firm expression, not forgetting to glare at Shinji at the end.
Mordred also joined in: "Yes, yes, this world is so beautiful, I haven't had enough fun yet, how can I let that bastard destroy it."
Being targeted by the two women, what else could Shinji say? He could only surrender obediently: "I'm sorry, it's my fault. I was judging others by my own standards. You adults should be more generous and don't bother with me."
"Then it is decided. Let's take back the Holy Grail together first, and then decide who will take it."
Fiore finally made the decision. For some reason, even though she was about to go to a dangerous battlefield, her face did not show the slightest bit of solemnity. Instead, she looked unusually bright.
"Without further delay, let's discuss the battle plan now."
The vast majority of the servants present had experienced battlefields, and more than half had served as commanders, so they were extremely efficient when discussing battle plans.
"The enemy's Noble Phantasm, the Sky Garden, has been under our surveillance, so it's not difficult to catch up. The problem is that the garden is suspended at a very high altitude. How can we get up there?"
"With my Hippogriff, I think I should be able to reach it, right?"
"My chariot is fine too."
"And Pegasus. One more thing to add, I can fly with the help of 'feather shoes', without riding Pegasus, and I can also carry another person if necessary."
The three Servants with Vehicles spoke up one after another. Chiron thought carefully about the appearance of the Noble Phantasm and shook his head.
"The Hippogriff and Pegasus can seat two people, and the chariot can carry a few more, but it's still a bit tight."
Avisbron suggested: "I can make a large flying puppet, but it doesn't have the speed and protection of a fantasy beast, and it's hard to resist the garden's defense mechanism."
"Ah, I have a way to deal with that. I don't mind attacks from magic at all! I have a book that can help me defeat any kind of magic!"
Astolfo pulled out a book from somewhere, but—
"Wow, it would be nice if I could remember the real name of the book, but since I forgot the real name, I still can't use my true power."
"Huh? You even forgot the name of the treasure?" Achilles was surprised.
"Hey, because my rationality has evaporated." Astolfo stuck out his tongue playfully.
"What a shame! Can you still be considered a rider?"