Fate/promise
Happened 10 years before the fifth Holy Grail war. The clash of seven masters with their servants, divided into seven classes: saber, lancer, archer, assassin, rider, caster and berserker.
The fourth holy grail war focuses the battle between the professional mages along with their servants. Six of the servants were summoned, the saber was left to be summon.
Hiro is a sixteen year old boy, and is terminally ill. He has 30 remaining days to live yet Hiro waited for the day of his death. Not until he accidentally summoned Saber, king of kings— Arturia Pendragon.
Due to his limited days, Hiro will make possible of the impossible. He will fight alongside Saber until his last ounce of strength.