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Summary

Chikyū Kaihō Gun ZAS (Earth Liberation Army: ZAS) is a vertical scrolling shooter that pushes the original Game Boy’s hardware to its limits. The game mimics the feel of classic titles like Gradius and R‑Type, but it adds a distinctive visual trick: the console’s passive‑matrix screen ghosting is used to fake transparency and multiple parallax layers, giving the impression of depth on a monochrome display.

Gameplay revolves around a single‑button ship that shoots, dodges, and collects power‑ups across five stages. The first four levels can be tackled in any order, while the final stage unlocks only after those are cleared, adding a modest non‑linear twist. Difficulty spikes are common, demanding precise timing to survive enemy patterns and defeat the hefty end‑level bosses.

The control scheme is praised for its simplicity, and the sprite work stands out with clear shading that separates background from foes despite the limited palette. Credits list Tadashi Nakatsuji as director and sound‑effects lead, with contributions from M. Nagashima, M. Takahashi, and others. The title saw a 2026 re‑release by ModRetro, bringing its niche charm to a new generation of handheld enthusiasts.

Storyline

In the 21st century, Earth becomes uninhabitable due to pollution, prompting humanity to abandon the planet and settle on Mars. The deserted world is later seized by a legion of super‑intelligent alien robots that remodel the planet into a habitat for themselves. A rag‑tag liberation force rises to reclaim Earth, aiming to drive the robots out and restore the planet. The game ZAS (often just called ZAS) follows this struggle, putting the player in the role of the resistance as they battle the robotic invaders and uncover the robots’ mysterious origins.