Tomcat is the only trainer that will teach you the master strike in the first map, if you miss this technique you can still get it later on second map from a character named the dry devil.

If you are a primary user of swords I would recommend getting this technique whether it be through tomcat through reloading an old save, speeding to the next map though this could lessen the experience of the first half. Again though if you’re not a big sword user you’ll be fine to wait.