Bushido is a triggered ability that increases the affected creature's power and toughness by a set amount when it blocks or becomes blocked.
Amy attacks with a Devoted Retainer, which has bushido 1, and Neil blocks it with a Grizzly Bears. After Neil declares the block, bushido will trigger and give the Devoted Retainer +1/+1.
- 702.44a. Bushido is a triggered ability. "Bushido N" means "Whenever this creature blocks or becomes blocked, it gets +N/+N until end of turn." (See rule 509, "Declare Blockers Step.")
- 702.44b. If a creature has multiple instances of bushido, each triggers separately.