Natsume 於 1990 年 8 月 10 日在任天堂 Famicom（紅白機）上推出經典動作遊戲《闇之工作人 KAGE》。在台灣，這款遊戲有兩個非常著名的「外號」。第一個是「水上魂斗羅」，因為遊戲第一關設計在風雨交加的輪船上，且支援雙人同時合作，其流暢的動作感讓當時玩家聯想到《魂斗羅》。第二個是「忍者外傳」，雖然與 Tecmo 的《忍者龍劍傳》系列完全無關，但由於主角同樣是高素質的忍者，因此被非正式地誤稱為忍者外傳。

在技術表現上，被公認為紅白機末期最強的動作遊戲之一。雙人合作模式非常流暢，兩名玩家可以同時進行高速動作而不會出現延遲。遊戲畫面充滿冷硬的科幻忍者風格，第一關「雨中戰艦」的動態雨水特效當時更是一大技術突破。音樂方面，由水谷郁（Iku Mizutani）作曲，節奏感強烈、熱血沸騰的電子音樂，至今仍被視為復古遊戲音樂的經典。

故事背景設定在近未來的 2029 年，美國被暴君「加魯達皇帝」鐵腕統治。為了終結暴政並為死難者復仇，伊賀派派出兩名頂尖忍者：颯（Hayate）與楓（Kaede）。需潛入加魯達守備森嚴的要塞，橫跨港口、地下道與摩天大樓等五大區域，最終擊敗皇帝並拯救人類。

操作系統方面，設計一套紮實且具有深度感的動作玩法。使用兩種主要武器：近距離高傷害的刀（Katana），升級後可釋放劍氣波；以及射程長、支援八方向攻擊的鎖鐮（Kusarigama），是安全通關的核心武器。忍者還能抓住天花板或欄杆進行倒掛移動或翻身向上，增加地圖探索的垂直維度。按住攻擊鍵蓄力發動「雷擊術」可以消耗大半生命進行強力攻擊，通常用於危急關頭或 Boss 戰。沿途還可撿拾手裏劍與手榴彈作為輔助遠程攻擊。

市場評價方面，被一致認為是紅白機動作遊戲完成度最高的作品之一。雖然難度較高，但精準的動作判定讓熟練玩家能享受如行雲流水般的操作快感。國際版本方面，美版稱為 Shadow of the Ninja，歐版稱為 Blue Shadow。2024 年，NatsumeAtari 旗下 TENGO PROJECT 推出重製版《KAGE～Shadow of The Ninja 絕影戰士》，在保留 16-bit 風格的同時大幅提升畫面與系統，再次點燃了老玩家的熱情。

Natsume released the classic action game Yami no Shokunin KAGE for the Nintendo Famicom on August 10, 1990. In Taiwan, it became famously known by two nicknames. The first, “Waterborne Contra,” arose because the opening stage takes place on a stormy ship and supports simultaneous two-player cooperation, evoking memories of Contra among players. The second, “Ninja Gaiden of the West,” emerged informally due to the high-quality ninja protagonist, though it has no direct relation to Tecmo’s Ninja Gaiden series.

Technically, KAGE is widely regarded as one of Natsume’s peak achievements in action games for the Famicom. Its two-player cooperative mode was remarkably fluid for the era, allowing both players to perform high-speed actions simultaneously without slowdown. The visuals reflect a cold, cyber-ninja aesthetic, with the dynamic rain effects in the first “stormy ship” stage representing a major technical breakthrough at the time. The soundtrack, composed by Iku Mizutani, is a driving, adrenaline-pumping electronic score that has since become a staple of retro game music.

The story is set in the near future, in 2029, when the United States is under the iron-fisted rule of the tyrant Emperor Garuda. To end his oppression and avenge the fallen, the Iga clan sends two elite ninjas, Hayate and Kaede, on a mission. Players must infiltrate Garuda’s heavily guarded fortress, navigating across five distinct zones including harbors, underground passages, and skyscrapers, ultimately confronting the emperor and saving humanity.

Gameplay emphasizes a deep and well-crafted action system. The player wields two main weapons: a katana for close-range high damage, which can unleash sword waves after upgrades, and the kusarigama, a chain-sickle with long reach capable of attacking in eight directions, ideal for safer navigation. Players can also perform unique hanging maneuvers, grabbing ceilings or railings to swing or flip upward, adding verticality to exploration. A charged “Thunder Strike” special move consumes roughly half of the player’s health, making it a last-resort option during boss battles. Along the way, shuriken and grenades serve as supplemental ranged weapons to chip away at enemies.

Critically, KAGE is celebrated as one of the Famicom’s most polished action titles. Its difficulty is high, yet precise controls allow for fluid, almost cinematic movement when mastered. Internationally, the game was released as Shadow of the Ninja in North America and Blue Shadow in Europe. Reflecting its lasting legacy, a 2024 remaster by NatsumeAtari’s TENGO PROJECT, titled KAGE: Shadow of the Ninja – Absolute Shadow Warrior, revitalized the game with enhanced graphics and updated systems while retaining the 16-bit aesthetic, reigniting excitement among longtime fans.