Those that are in the middle of your heart are the ones you have the most loyalty towards. The middle of your heart is the most sacred, special place for people, so it makes sense that those you keep in the middle of your heart are those you are most loyal to.
You pictured Chewbacca (ちゅう), didn’t you? No? Well you should have. Chewbacca deserves everyone’s loyalty. Chewbacca is super loyal to you, so he deserves your loyalty back.