Slash weapon rank
A weapon can have letter ranks in slash, pierce, thrust, and strike. These ranks interact with enemy vulnerabilities to determine the chance of unbalancing an enemy when the attacker has a combat link. A successful unbalance can enable a link attack.
How it works
For Cold Steel III and later, the supplied mechanics excerpt gives rank base chances of SS 25%, S 15%, A 10%, B 5%, and C 3%, before applying the vulnerability star rating. The excerpt does not identify a character's slash rank.
When it helps
Check an enemy's vulnerability and the equipped character's displayed weapon ranks when considering an unbalance opportunity.
The tradeoff
The chance also depends on the vulnerability rating; the evidence does not supply named character ranks or guarantee an unbalance from a rank alone.
Your next step
Use the in-game enemy and character details to check the relevant rank and vulnerability.
Read the supporting references
Check the edition and source version for patch-specific details. Guide methodology.