The Master is met at the Beach, and can teach Martial Arts.
Meet the master
Prerequisites: Summer, access to the beach, Tuesday, Thursday or Saturday 10:00 - 16:00, 50% chance, don't know the karate skill
Mike will meet a strange men who introduces himself as "The Master". He tells Mike that he can teach him the ancient ways of martial arts.
If Mike accepts he can now train with The Master.
After Mike trained with the master a couple of times he will reach 100% in the martial arts skill. That does not mean that he learned the skill yet.
Finish your training
Prerequisites: done meet the master, Beach, train with The Master, Martial arts progress = 100%
The master tells Mike that there is nothing he can teach him anymore and after a quick training fight Mike learns the martial arts skill.
Outcome: Mike learns martial arts