The 'Lone Goat and Kid' story is great. It shows Usagi's honor and his sense of justice. In this story, he has to protect a young goat and its owner from various threats. It delves deep into his character, and the interactions between Usagi and the other characters are really well - written. There are also some intense fight scenes that keep you on the edge of your seat.
One of the best is 'Grasscutter'. It's a story full of adventure and honor as Usagi gets involved in a quest related to a powerful sword. The art in this story is also amazing, really bringing the feudal Japanese setting to life.
I'd recommend 'Usagi Yojimbo: Yokai'. It has a simple yet engaging plot that introduces the main character Usagi and the world he lives in. It also has some cool encounters with Yokai, which are Japanese supernatural creatures. It's a great way to get into the Usagi Yojimbo series.
Another great beginner - friendly story is 'Usagi Yojimbo: Senso'. It gives a good introduction to Usagi as a character. It's set during a war, and Usagi has to make some tough decisions. The story is not overly complicated and is a great way to get into the Usagi Yojimbo series.
One common theme is power exploration. Fans often write about characters discovering new powers or mastering their existing ones better. For example, in many fanfictions, the main character might find a way to combine different elemental powers.
It's mainly about a story involving magic and family. The protagonist has certain powers related to the wind and there are complex relationships and battles within the story.