The 'How Not Summon a Demon Lord' manga is the original source, providing more background and nuances. The anime adaptation makes it more accessible with dynamic visuals, but might leave out some minor details for time constraints.
Overall, the manga offers a deeper exploration of the world and characters. The anime does a decent job of adapting the key moments, but for a fuller experience, the manga is better. It has more panels and text to flesh out the story.
First, you need to have a deep understanding of the original work's characters and world. Then, come up with an interesting plot that fits within that framework.
Overall, the ending of the manga was well-structured. It tied up loose ends and left fans feeling content. The resolution of conflicts and character developments were handled smoothly.