From Alpha Manga:
After a grueling battle, the magic knight Kyle finally defeats the demon lord or so he believes. He wakes up to find himself in the land that had been destroyed in his past life. He is reunited with the precious person he thought he had lost forever. To stop the human world from being destroyed again, along with his friends, Kyle uses his memory from his previous life to once again save the world! A fantasy saga about a brave knight.

Original WebComic