"Do, mi glywais i'r stori."

Translation: Yes, I heard the story.

[Squonkalini]

What is the function of "mi?"

[ibisc]

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

[Squonkalini]

Got it, thanks!