Barakamon, Dororo Recommendations
Main character has a smaller kid following him around.
In Dororo: Hyakkimaru is always being companied by Dororo.
In Barakamon: Sei is always being followed by Naru.
True, Barakamon is not action, but the main characters with younger "siblings" around kinda give off the same vibe.
Dororo is on the other hand, a very dark story compared to barakamon, but very similar with the bonds of it's characters. Sei and hyakkimaru are on a mission to accomplish something, no matter what it is, will let no one hinder their tasks. This makes both of the characters alone in some sort of way. That loneliness changes when a little kid starts hanging around with them for a little while, till it is admitted by the main character (directly or indirectly) that they enjoy being friends with them or they can't live without them. Now as I may explain it, I'm not