What do you mean the explosion is over? Has the protagonist become a robot?

Yes, the protagonist Jack is transformed into a robot, which is a sad story.

About the background of the whole story:

This story takes place in the future. In 2 179, Xada, a virus that can survive in outer space, came to earth in the form of semi-organic and semi-inorganic meteorite polymer Aza. After 12 hours, the first infected mutant appeared in the world. Since then, Xada has gradually spread with the attack of infected varieties on humans and other organisms. After forced mutation, infected creatures abandon their original physiological characteristics and become terrible monsters with strong viability and strong attack tendency. In the face of this sudden powerful monster, human beings are on the run. At that time, the first generation of neural control mecha Warmech was only in the testing stage, and it could not resist the infected variants at all. The resistance lasted only a year. In 2 180, the remaining human beings abandoned their home planet earth, which has survived for tens of thousands of years, and evacuated from the outer space colony Gaia through the portal system.

In this global evacuation, not everyone can go to Gaia safely, and some people stay on the earth forever because of Xada. According to statistics afterwards, the number of missing persons is close to1.700 million. In fact, a few people still live on the earth. They are the people who failed to evacuate for the first time, and some of them voluntarily stayed on the earth. They hope to put themselves in their shoes and find a way to deal with Xada. However, many people have become variants of Xada infection and integrated into the Xada army.