The "Seal the Devil, Lock the Immortal" section in the Divine Grave Chronicles is one of the more challenging parts of the game. Below, I will provide a walkthrough for this part of the game.
Small Tips for Passing "Seal the Devil, Lock the Immortal"
Use infantry generals leading flying troops. Why should you use an infantry general leading flying units placed at the front when fighting four magic-based units? Because flying units have a resistance 5 points higher than infantry and also have a higher chance to dodge attacks. This makes them very suitable against magic-based units. You can conduct a test: try using an infantry general leading flying units versus one leading regular infantry units at the front and see if the flying units can withstand more hits. For example, if the infantry could only withstand two hits originally, now it might be able to take three. (Additionally, magic-based generals have the same resistance as flying units, so using magic-based units instead of flying units at the front works just as well. All other unit types have 5 points less resistance compared to magic or flying units.)