Kazuma is one of the main characters. He is a typical NEET who gets transported to a fantasy world. He's not your typical hero, which makes him really interesting.
In Konosuba Vol 6, Kazuma is the leader - like figure of the group, trying to keep everyone in line. Aqua provides a lot of the comical relief with her lack of practical skills. Megumin's explosive magic is a key part of their combat strategy. And Darkness adds an interesting dynamic with her masochistic tendencies. Their different personalities clash and combine to drive the story forward in this volume.
In volume 5, one of the main plot points is the group's encounter with new challenges in the fantasy world. They might face stronger enemies or difficult quests.
Well, in the light novel, there's often more in - depth exploration of the characters' thoughts and backstories. The author can spend a lot of time delving into Kazuma's inner monologues about his situation in this strange world. However, the manga might simplify some of these aspects to focus more on the comical and action - packed scenes. Also, the pacing can be different. The manga might skip over some minor details from the light novel to keep the story flowing at a faster pace for its visual medium.