Best for
Sword is an option for increasing critical hit frequency when you have a limited weapon collection. It does not provide basic attack unblockable chance, so consider which of those benefits your fighter needs more.
Best users
Give it to an attacker who already gains extra critical damage from another source. The additional chance helps that fighter use their existing critical damage bonus more often.
When it is useful
It is less useful against enemies who are protected from critical hits. Even against a suitable target, the chance bonus does not make every hit critical.
Best pairings
Pair it with equipment that increases critical damage. If enemy blocking is also a problem, add a separate source of basic attack unblockable chance; the critical hit bonus does not replace it.
