What Shinji has to do can be simply summarized in one sentence - to cheat in this world, no, to open up the magic circuit.
Although the self in the other world and Shinji cannot be considered the same individual in a strict sense, but facing a being with the same appearance, the same background, the same body, similar experiences, and even such similar thoughts, how can I really treat the other person as an unrelated stranger
If the life in this world is happy and complete, and there is no need for external intervention, it would be fine. Just take a look and leave quietly. But the Matou family in this world is even more decadent than the world where Shinji lives, and the desire of Matou Shinji in this world for the magic is even more determined.
Seeing himself like this, Shinji couldn't just sit there and watch.
Yustisa gave him a chance and a brand new future. He also wanted to give himself in this world a chance and take a different path.
So there is a scene where the young version of Shinji and the childhood version of Shinji open the magic circuit.
Magicians who have a little knowledge of the magic world know that opening a completely closed magic circuit is a thankless task. Not only does it consume a huge amount of magic power - the magic power of an ordinary magician can be regarded as a common vehicle engine, but the magic power required to open a closed magic circuit is a nuclear reactor. It also carries great risks - the output of a nuclear reactor is not something that ordinary vehicles can withstand. If you are not careful, the car will be destroyed and people will die.
Even an ancient family with a long history might not be able to afford such a huge price, let alone exchanging it for a magician with an uncertain future. It was a loss no matter how you looked at it. Only Yustisa, who was desperate, was willing to take a gamble.
But Shinji had no such concerns. Most of the huge amount of magic power consumed to open a closed circuit was wasted. Because he didn't know the target magic circuit, he could only try again and again to find the correct path. But Shinji was different. His target was himself in another world with the same magic circuit. He didn't even need to think about it. He could find the correct path by instinct.
And because it is his own magic circuit, he is very clear about the limits of the circuit. He does not have to worry about excessive output bringing adverse effects to the body, nor does he have the rejection caused by the invasion of foreign magic power, thus maximizing efficiency.
As for the output of "Nuclear Reactor", it is not a problem for Shinji who has the body of a Servant. The body of a Servant is made of magic power, and Shinji knows the skill of "Magic Release". He may not be much worse than Yustisa with the help of the Holy Grail when he bursts out the maximum output in an instant.
In other words, only Shinji Matou, who becomes a Servant, can accomplish the project of opening up the magic circuit for another world on his own without any risk.
The project is complex to explain, but the actual operation does not take too much time.
The huge magic power that was passed down from one line to another continuously washed the boy's magic circuits in an extreme way, opening up the innate blockades while also causing him great pain. If I had to describe it, it was like a sledgehammer hitting your body at a rate of once a second, making you swollen all over but keeping you awake to experience the pain.
Unexpectedly, the willpower of this self in this world was very strong. Despite enduring such extreme pain, he just clenched his teeth tightly and did not make a sound, even though his whole body was covered in cold sweat, veins were bulging, and his lips were bitten and bleeding.
"I never thought that the decline of the Matou family would strengthen your will. Very good. Those who achieve great things not only have extraordinary talents, but also perseverance. With this will, you will definitely have a place in the future world of magic."
Shinji gave great affirmation to this persistence. Judging from willpower alone, the boy's performance is even better than he was back then.
As Shinji laughed, his stored magic power quickly dissipated, and the time he could stay in the real world was reduced from two days to less than half a day. This effort also brought enough rewards, and all 32 magic circuits were connected.
As Shinji withdrew his hand, the boy also lost consciousness - he had already reached his limit and was holding on with just one breath. When the pain disappeared, the breath was gone as well.
After putting the coat on the boy and using his limited magic power to carve an "EIHWAZ" rune on his forehead, Shinji shifted his gaze away from the boy and moved towards the corner connecting the courtyard and the house.
"Sleep, sleep. When you wake up, the world will be different, and your life will be different too—don't you agree, Matou Zouken?"
A skinny old man with a big head and a small body, like an alien, walked out from the darkness with a cane. Once you see this, you will never forget it. It was Zouken Matou who was killed by Shinji in another world.
Zouken bowed tremblingly to Shinji: "Thank you for your kindness to Shinji and the Matou family."
"Forget about these useless courtesies. I did this because I like this child. It has nothing to do with you or the Matou family."
Shinji snorted coldly. He always hated Matou Zouken and naturally would not give him a good face.
"Shinji is my grandson after all, and as his grandfather, I should express my gratitude to him."
The old man's expression didn't change at all, and he didn't seem to mind Shinji's arrogant attitude at all.
"Sir, please feel free to ask for anything you want. The Matou family will do their best to satisfy you."
Shinji narrowed his eyes and said pointedly, "Do your best to satisfy? When did the famous founder of the three great families, the great magician Machiri Zorgen, become so easy to talk to?"
Zōken's old face finally showed some emotion: "To be honest, sir, I should have died after the Holy Grail was taken away. I just couldn't let go of the declining Matou family, and I also wanted to know what the Holy Grail would become in the end, so I stayed alive until now. Now I am just an old man who is not much stronger than an ordinary person. In front of you, I am as fragile as a bug."
Shinji turned on his senses to the maximum and locked onto the old man in front of him recklessly: "More than sixty years have passed, and your injuries haven't improved at all? Your insect magic may not be good at other things, but it is definitely world-class in healing and prolonging life."
"I don't deserve such praise from you, sir." Zang Yan was still not angry, his attitude was as humble as ever, but there was a little more sigh in his words: "But it is indeed as you said, I don't care about the physical injuries, but my injury is in my soul. The magician who stole the Holy Grail is proficient in soul magic, and he left me with irreparable injuries. Since then, I have been no different from a useless person."