If you have trouble with fighting games, or if you just want to save time, you can use my save state.

Simply copy the file into the game's user folder in your Steam installation directory.
By default this is:
C:\Program Files (x86)\Steam\userdata\<User ID>\999660\remote\

Start the game, choose Samurai Shodown 1, press Start and load the save.

You end up in the final boss fight against Amakusa. Just survive the last 5 seconds, or give him the final blow.

You get:

A Worthy Opponent

And if you don't have it by now, you will also receive:

The Wandering Swordsman

Amakusa's Fall

Have Fun.

https://drive.google.com/file/d/1xpTuR7ZwOoUI4IHoERCJN6LdF01E8MGB/view?usp=sharing