It is just a positive marker particle that can be put in front of a positive statement as opposed to a question or a negation. You may also see fe used in the same way. Both cause soft mutation.
- Do, ces i fy nhalu ddoe - Yes, I was paid yesterday
- Do, fe/mi ges i fy nhalu ddoe
Sometimes the mutation remains even when the fe/mi is omitted, especially with ces i, cest ti, caeth e, etc.
- Do, ges i fy nhalu ddoe