From author's description: "Immortal Defense is a fresh take on the tower defense genre. In the course of your adventure, you'll face twenty-six different enemy types, including challenging bosses. You'll come to know the use of eleven different "Points", each with its own personality and style of defense. You'll go through one hundred stages of challenging gameplay--including secret stages for the most advanced path defenders.
You'll experience an interesting combination of procedural and pixel-art, an original soundtrack, and you'll explore a story about love, duty, and the consequences of immortality. With six to ten hours of gameplay, this game won't be something you play and then forget about.
What would you be willing to defend for all eternity?"
A walkthrough by the author is available on the site's forums, here.