I've just finished reading the main story. Should i read the side story? Does lucien evans still appear frequently in it? How is it compared to the main story?
nope. It happens in the future and a newbie tries to find a field Lucien did not set a cornerstone. So it's not about Lucien but the after-effects of his involvement.
That's such big bananas~ (has no idea what's going on but was notified that @Effugium made a thread) O.O)?
Side story is about his kid and his friend as they explore world of dead and effects Lucien left on the world. so if you are curious you can read it. Quality is as good as main story. There is another side story that mentioned how city in the sky was formed by Douglas. That is a prequel before Lucien appeared.