Ezra and Saber are put in a situation that their bodies can transfer the same injuries they absorb to their loved ones like Jellal and Shirou. They both have to fight each other to the final blow.
So if Saber Dies, Shirou Dies ( Fate/stay night ) But If Shirou Dies, Saber Dies
And Ezra Dies, Jellal Dies ( Fairy tail ) When Jellal Dies, Ezra Dies
Letting you know Shirou and Jellal can't fight nor assist the uses of magic or abilities, etc.
Only Saber and Ezra fight can each other.
With their Skills, Abilities, and Weapons over head under the belt of there experience of their lives and Arcs.
Post here of what you think!