I tend to make my characters have a lot of emotional depth, so the hardest for me is a static side character who doesn't really feel things a lot and is just very laid-back with no character development. It's hard to figure out what he'll do next because he doesn't have that depth to him like my protagonists do. It's quite frustrating.
Also, when I collaborate, it's very hard to write characters I don't create because I don't know what my partner intends to do with them…
