Books like Parasyte by Foltz Design

"The crazy world of Gantz just got a heck of a lot crazier! First, there were people being recruited at the moment of death to fight aliens living on earth, but unseen by humanity. The battles seemed to take place outside of human sight. Our reluctant hero, Kei, has lived through many of these battles, but now something strange is happening. People can see the Gantz warriors! This ragtag collection of street punks, fighters, and school kids (and a fashion model and a panda) are suddenly exposed to the world, along with the freakish aliens they fight. Will the civilians believe what they see, or are their lives so full of media that they think it's just fantastic 3D entertainment?"--Amazon.com.

Ichiro Inuyashiki is down on his luck. While only 58 years old, his geriatric looks often have him written off as a pathetic old man by the world around him and he’s constantly ignored and disrespected by his family despite all that he’s done to support them. On top of everything else, his doctor has revealed that he has cancer and it appears that he has little time left in this world. Just when it seems things couldn’t get any worse, a blinding light in the night sky strikes the earth where Ichiro stands. He later wakes up to find himself unscathed, but he soon starts to notice that there’s something…different about himself. However, it turns out that these strange, new changes are just what Ichiro needs to take a new lease on life and now it seems like there’s nothing to stop him from being a hero worthy of the respect that he never had before…unless, that is, there was someone else out there with these same “changes”…

Killy is a man of few words who packs one very powerful gun. He wanders an endless labyrinth of cyberdungeons filled with concrete and steel, fighting off cyborgs and other bizarre silicate creatures.