The Crest of Cichol grants a 50/30/15% chance to prevent enemy counter attacks when using a combat art. Like most other things in Fire Emblem, this is determined with a random number roll. It was determined through manual testing that combat arts like Swift Strikes will cause the game to roll twice to see if the Crest of Cichol effect will activate. If either roll works out, the Crest will activate and the enemy will be unable to counter.

The two natural bearers of the Crest of Cichol are Seteth (major), and Ferdinand (minor). They both also happen to have access to Swift Strikes by raising Lance Rank to A. Hence, they are both able to take advantage of this.

Let's say that \(x\) represents the probability that the Crest of Cichol activates for a single roll. Then, we can say that the probability of not activating is represented by \(1 - x\). Since Swift Strikes rolls twice, the probability of the Crest not activating for both rolls in a row can be expressed as \((1 - x)^2\). Therefore the chance that the Crest of Cichol activates for at least one out of two rolls (activating twice doesn't make a difference) is \(1 - (1 - x)^2\). Plugging in the values of \(50\% = 0.5\) for Seteth and \(30\% = 0.3\) for Ferdinand yields the following.

So, Seteth has a 75% chance to not get countered when using Swift Strikes, and Ferdinand has a 51% chance. That is borderline reliable.