Tsugumi Project summary:

Leon, an elite soldier from a militaristic Europe, was forcibly embarked on a secret expedition. In a ruined Japan, abandoned for more than 200 years, he and his companions in misfortune must recover a terrifying weapon. Its code name: Tsugumi. All we know about it is that its destructive potential is such that the world has preferred to crush the archipelago under a shower of atomic bombs rather than see its development completed...

But the operation turned short: the plane crashed, and Leon found himself alone in Tokyo Bay. Hungry, at the end of his strength, with only one anti-radiation suit for protection, he quickly discovers that the city is not as deserted as expected...