Though only looking out for himself, Toshiro ended up saving all of Kamigawa.

Toshiro Umezawa

Bushido 1 (Whenever this creature blocks or becomes blocked, it gets +1/+1 until end of turn.)
Whenever a creature an opponent controls dies, you may cast target instant card from your graveyard. If that spell would be put into a graveyard, exile it instead.

Secret Lair Drop

Betrayers of Kamigawa

Bushido 1 (When this blocks or becomes blocked, it gets +1/+1 until end of turn.)
Whenever a creature an opponent controls is put into a graveyard from play, you may play target instant card in your graveyard. If that card would be put into a graveyard this turn, remove it from the game instead.

You must still pay the mana cost of the target instant in your graveyard to cast it using Toshiro’s ability.

Creatures destroyed by an instant that you cast normally can cause a trigger that allows the instant to be cast again. For example, cast Terror on an opponent’s creature. The creature is destroyed, triggering Toshiro’s ability, and then the Terror is put into your graveyard. You can put Toshiro’s ability on the stack targeting the Terror and then recast it when the ability resolves.