Reinforcement

Reinforcement (強化 kyouka) is the most difficult magecraft with the purpose of pushing a basis to the utmost.

It is the foundation of all magecraft that enhance the existence of the target by pouring prana, but as no clear expression of how much it can be enhanced is defined, almighty reinforcements are rare. It is the same as adding something to an object that is already complete, in case of failure the target will receive it as a poison. Success requires a good grasp of the inner structure to fill openings with prana.

Reinforcing the purpose of existence would be increasing the sharpness of a knife, the nourishment of food, or the moe factor of a maid. It is impossible to reinforce something vague. As living things will resist invasion of your prana, reinforcing someone else is the hardest.

By putting this in application, Emiya Shirou is able to create a bow out of the branch of a tree, repair a soccer ball, or change the shape of an object.

Source: based on the Fate/Side Material encyclopedia entry (p.58)