I'm looking for a manga I read in physical copy at my local library about a year ago. It's a military (sci-fi maybe) story in a war between fictional countries (maps of the countries and the war situation are shown). I only remember the very first pages:

A soldier and his battalion advance into a jungle area. They lose most men while moving through the jungle. They reach a beach where the enemy has landed/is waiting. His last comrades get killed. He's saved at the last second by a young boy (looks like a 10-year-old) who is actually a cyborg/robot weapon (I think he had big robot hands) made for killing.

The boy quickly and brutally kills all the enemies. The soldier realizes the kid is a secret weapon from his own side/country. He immediately asks to join/follow the boy team because he have one.

Thanks for your help