FATE/Probability

Under the faint morning sunlight and snow, Shirou spent the weekend morning doing physical activities while opening and closing his magic circuits while kiritsugu watched him. 

After finishing his workout kiritsugu called him to the dojo. Inside the dojo, the pair sat face-to-face and kiritsugu said

"As you have mastered the opening and closing of magic circuits and your pain from newly open circuits has passed we will start talking about mage craft.".

opening the notebook they used last time he asked 

"As you must have remembered I told you that the life force of the planet is mana and leylines act as the planet`s veins so where else do you think we can source mana except for the environment?"

Shirou pondered for a while and answered

"We and all living beings contain life force can't we use that as mana."

"Yes, we can." answered kiritsugu and then continued 

"While an ordinary person has lifeforce that can be extracted in the form of mana, it is not replenishable naturally and is of minuscule quantity as well as very impure." 

kiritsugu gave Shirou a sharp look before continuing 

"People with active magic circuits can use their life force and convert it to mana using the circuits and we call this "Od". People born with more magic circuits naturally have higher od."

"And Shirou you especially need to learn how to use mana of the atmosphere as due to your lack of any significant lineage you possess just above average od." said kiritsugu while drawing a diagram on the paper.

Looking at Shirou kiritsugu smiled and said 

"Od when used is slowly replenished from the ambient mana by the magic circuits. It can also be replenished by transfer of mana from another magus."

The father and son discussed lesser sources or od and the greater source or Gaia till noon and Shirou learnt a lot. He also felt as if he had started walking on the path of true magecraft.

He listened to the lesson till he had to reluctantly go to prepare lunch. Looking at Shirou leave kiritsugu started writing about things to teach to his student Taiga.

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….

While Shirou was preparing for the last week of school before the winter break the twilight came. he went to the kitchen to prepare snacks and tea for kiritsugu and Taiga.

As expected taiga came within half an hour and Shirou quickly put the snacks on the table and left. While kiritsugu was busy Shirou opened the notebook kiritsugu uses to teach mage craft and remembered his father's word

" Shirou now that you have achieved control of your circuits as well as felt your od, come to the lawn after Taiga goes home we will find out your origin and element."

While thinking about elements and origins he came across the notes about roots. it stated 

"The root/ the swirl of root/ akashic records is the origin and end of everything in this universe. The root is where everything came from and where everything will go including our souls."

"Root is not a physical place in this world but a metaphysical realm where every concept we know about came from and will go back to after its material container is destroyed."

"Magi aim to reach the root and obtain magic so all they mage craft in essence are the families own way to reach the root."

"What is this magic and what are the origin and elements?" Shirou wondered out loud and looked at the time.

Seeing it was already late he went to prepare dinner and meanwhile, taiga left Emiya's residence grumbling that she didn't need to always talk in English.

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….

After having an early dinner kiritsugu pulled Shirou out onto the lawn and made him sit.

While drawing a magic circle on the ground using a silver knife he said 

"Do you remember about the root?"

"Yes I do," said Shirou and then kiritsugu asked 

"Then you must remember that everything comes from it even our souls, but the root is not a physical phenomenon so what part of our soul comes from it ?"

Shirou thought for some time before replying 

"The elements?"

"No" replied kiritsugu and continued 

"The origin is the answer, what concept left the root and became our soul is called the origin."

"Origin is often expressed as a core personality trait in the person. An origin can be anything and most of them are abstract and very hard to define."

"For example, my origin is severing and binding. This leaves me with a poor aptitude for fixing things, for example, if I tried to fix a broken machine it will most of the time I would make some mistake and it would not be fixed."

"I don't know more about them because I didn't have any formal education in magecraft."

"So what describes origin best is the sentence. What concept defines your core personality as well as you as a person is your origin"

When this explanation ended kiritsugu had completed the magic circle and said 

"This ritual here will give me a feel of your elemental affinity and a vague feel of your origin when you sit in the centre and circulate your od through the circuits."

Nodding his head Shirou stood up and moving to the centre of the ritual circle sat cross-legged. 

The scene of the hammer strike flashed past his mind and his circuits opened up giving a feeling of slight heat on his skin.

He earnestly began converting mana in his circuits and lost himself to the increasing heat he felt from his circuits.

Kiritsugu closed his eyes and focused on the feedback of the ritual circle. He tried to give a name to the vague feelings he was feeling.

Time passed and by 15 mins Shirou was already sweating profusely and felt as if his magic circuits were burning his skin and kiritsugu was lost in his thoughts

kiritsugu mocked himself in his thoughts and then continued to perceive Shirou`s element.

Opening his eyes kiritsugu said 

"That's enough Shirou you can stop".

Hearing that Shirou let out a breath of relief as he slumped down after closing his burning circuits. Witnessing this kiritsugu said 

"We have to train your circuits a lot if you want to be able to maintain the combat state for long periods. Now go sleep we will talk about your element and origin tomorrow morning."

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…

Waking up Shirou felt a phantom heat as if his circuits were burning, then he snapped out of that and resolved in his mind 

Preparing the breakfast and serving it shirou excitedly asked 

"Dad what is my origin and what are elements?"

"First let's talk about elemental affinity, the affinity is the predisposition of a soul towards performing certain mysteries and hence giving ease as well as boost to results when performing them." answered kiritsugu and continued

"According to clock towers, there are 5 common elements fire, earth, water, wind and ether or void."

"Fire is not just about flames but Spells of the Fire element are related to consumption, heat, entropy, fuels, energy transfer and thermodynamics."

"Water element has mostly spells related to flows, forms, cycles, combinations and manipulations."

"Earth element is about grounding, cultivation of energy and energy embedding."

"Wind-based spells deal with air, kinetic forces, static energy, free energy and directed movement."

"The final element of ether is amorphous and incapable of materializing by its own power, it is what allows shapeless bodies to take a material form, it combines itself with any of the other four Elements to actualize the mysteries of Thaumaturgy."

Taking a deep breath kiritsugu said 

"Your element as well as the origin is sword and you also have some affinity to fire with a specific affinity for reshaping, heat and change."

"What does elemental affinity for sword mean?" asked Shirou confused as his affinity is about none of the 5 mentioned elements.

Kiritsugu then explained to him how specialised elements are common but hard to master due to the passing on of mage craft by generation.

He also talked about how he doesn't have any particular magecraft for Shirou`s affinity and Shirou would most likely have to make his own. 

After learning about how even with the detriment of affinity and the origin being the same, it can be used to make unconventional magecraft-related to them stronger sparking resolve to make his own craft.

Shirou understood the nature of mages to some extent as he had nearly watched ⅔ of the holy grail wars in his dreams and the modus operandi of magi made him understand the blood-stained and fascinating world of magecraft.