I think the backstory behind the characters may not be very deep, but don't let that take away from the fun of the show. The way the characters grow in each episode is very noticeable and important for the dynamics of these characters. I think it's a good show with interesting concepts and ideas. Let's start with the swords- I like that they introduce multiple swords with unique abilities that also symbolise the importance of the bonds between the main characters. It also emphasizes how they are able to support each other differently. If you look at the show objectively and not in depth then you can say it's "boring" or that the main characters are "shallow", but the approach that it is clearly taking is to not focus on the backstory to much and to more so focus on the growth of the characters throughout the show and how they develop. Each character has a smaller story which has their past as a foundation, and is built upon how they deal with these situations in the present and move past them while helping others to not make similar mistakes. I think this is more so a show of growth. I personally look forward to see how these characters grow mentally and in strength in future seasons and episodes. (If any future seasons or episodes come out.)