Star Wars: Guardians of the Whills

Greg Rucka is one of the coolest Star Wars author to mostly dabble in young adult and junior novels for it. They're honestly a pleasure for either age, so you don't need to be scared off by the “junior” tagged to this one.

This (relatively short) book follows a pre-Rogue One story featuring Chirrut and Baze, and it does a wonderful job of making you care about the secondary characters and give you more character info (as well as on their relationship) between those two.

I wish all of the other members had books like these (though of course I still need to get to the Jyn one) because if they could all be like this, then excellent.