《太空戰士4》（Final Fantasy IV）是由史克威爾（當時為Squaresoft）開發，並於1991年首次在超級任天堂（Super Famicom）上發行的角色扮演遊戲。是該系列的第四部作品，對整個RPG遊戲類型產生深遠影響，也被認為是系列中最具開創性的作品之一。不僅在劇情深度、角色發展和遊戲機制上有顯著的進步，還引入許多影響後來角色扮演遊戲的創新元素。之後有移植到DS、手遊、Windows。

故事發生在由四大元素（火、水、風、土）支配的幻想世界，主角是塞西爾（Cecil Harvey），曾是巴倫王國(Baron)國王麾下的紅翼隊長黑暗騎士。在遊戲開始時，塞西爾被派遣去取回名為「水晶」的神秘寶物，任務是為幫助國王奪回寶物。在受到國王指令轟炸敏西迪亞鎮搶奪水晶後，良心不安的質疑國王動機後被免職，並與凱恩(Kain)攜帶包裹往迷霧村前進。當抵達迷霧村時，怪物從包裹內飛出並摧毀村子，只剩下另一個主角莉迪亞(Rydia)存活，情急之下莉迪亞使用招喚獸泰坦引發地震，而塞西爾也與凱因分散。於是兩人開始踏上尋找水晶的旅程。之後，塞西爾的內心充滿矛盾，他開始質疑國王的命令，並在一次行動中發現自己所效忠的國王竟然是利用水晶來達到控制世界的目的。

隨著劇情發展，塞西爾決定背叛原來的國王，並與不同背景的夥伴們聯手，開始拯救世界的冒險。這些夥伴包括擁有強大白魔法力量的弓箭手羅莎（Rosa Farrell）、來自Mysidia的傳說賢者泰拉（Tellah）、勇敢的武頭僧楊．房．萊頓（Yang Fang Leiden）等，這些角色各自擁有不同的動機和背景，並且隨著故事的推進，彼此間的情感和關係也不斷發展。最終，塞西爾和他的夥伴們發現，水晶的背後隱藏著更大的陰謀，而他們所面對的敵人不僅僅是邪惡的國王，還有來自另一個世界的威脅-名為高拉（Golbez）的黑暗巫師，他正企圖利用水晶的力量重塑世界。

在劇情方面加入許多複雜的角色發展和情感描寫，這是當時RPG遊戲中的一大創新。情節充滿犧牲、友情、背叛和救贖等元素，對人物進行深入的刻畫，使其不僅僅是一場單純的冒險，還是關於命運與選擇的深刻探討。遊戲舞台有分地球及矮人存在的地底世界，在遊戲後段，取得改造太空船後即可飛行到人造月亮，最終boss及最強招喚獸巴哈姆特也在那等著主角到來。

初期需要注意的是塞西爾需要打敗自己內心的黑暗自我，成為聖騎士(Paladin)後，主角級數也會歸0，因此初期經驗值不需太積極提升。而對敵方的攻擊力而言，招喚獸比較實用，但對MP的流失也較高，若能早點學習到終極黑白魔法則對全破速度較有幫助。

在操作上繼承該系列的經典要素，但也進行部分創新和改進。最顯著的改進是引入「Active Time Battle」（ATB）系統，這使得戰鬥不再是傳統的回合制，而是更具動態感和即時反應的系統。每個角色的行動需要等待一段時間，這段時間由角色的ATB條來決定，當ATB條充滿時，可以選擇角色的攻擊或技能。這系統讓戰鬥更加富有節奏感，也增加戰術的多樣性。

基本操作指令分別有1.物品(Item) 2.魔法(Magic) 3.裝備(Equipment) 4.狀態 (Status) 5.隊伍的排列(Order):魔法師或是召喚獸師應該放在後面，避免敵人密集攻擊 6.前後排列(Row):血量較少的最後放後排 7.相關設定的調整(Config) 8.快速存檔(Quick save) 9.存檔(Save):須注意通常在敵人洞穴中是無法存檔，除非有出現儲存的地方。

角色有各自不同的職業和技能，並且每個角色的成長都與其職業密切相關。與前作不同的是，角色並不會進行自由的職業選擇，而是依照劇情的發展，自動更換職業。此設計使得每個角色的技能和能力都有其特定的發展路徑，並且能夠在不同的情境下發揮出不同的作用，強化遊戲的策略深度。此外，還加入「召喚獸」的元素，在戰鬥中召喚強大的生物來協助戰鬥。這些召喚獸都有獨特的技能和威力，根據戰鬥情況來選擇最合適的召喚獸來對抗敵人。

在此遊戲設計中，最強的並不是魔法，而是召喚獸。需要設法取得散落在各地的招喚獸，取得後可以對敵人進行全體攻擊或是我方補血。初期主角除攻擊以外，還可以使用Dark的招數，對敵人集體攻擊，但是也會大量失血，變成聖騎士後就能使用魔法。夥伴凱恩則可以使用跳躍(Jump)，雖然攻擊力強，但是開大招的時間比較久。莉迪亞(Rydia)可以使用黑白魔法及召喚獸召喚，後期升級比較困難，之後女主角蘿莎(Rosa)及西德(Cid)都會陸續因劇情發展加入。

世界設計分為多個不同的地點，包括城鎮、地下城和各種奇幻的地形。每個地點都有其獨特的背景和挑戰，並且隨著劇情的發展，會解鎖新的地區。探索元素不僅限於尋找物品和解開謎題，還包括與NPC的互動和支線任務的完成。這些支線任務通常涉及到額外的角色發展和強化角色的能力，並且提供豐富的遊戲體驗。地下城設計巧妙，通過解謎、戰鬥和策略來逐步前進。某些地區會包含隱藏的寶藏和強敵，這些都需要精心探索來發現。關卡設計不僅富有挑戰，也充滿探索的樂趣。

當年自發行後，獲得極為正面的評價。遊戲的劇情、角色塑造和創新的ATB戰鬥系統受到玩家和評論家的廣泛讚譽。它被認為是角色扮演遊戲的重要突破，尤其在故事情節的表達上，相比於之前的作品，更加深入人心。背景音樂也得到高度的評價，由植松伸夫（Nobuo Uematsu）創作的原聲音樂至今仍被視為遊戲音樂的經典之一。然而，戰鬥系統和某些線性設計也受到部份批評。有些玩家認為，遊戲的某些部分過於強調戰鬥和劇情，缺乏更自由的探索元素，不過這並未嚴重影響其整體的好評。

當時在商業上同樣取得成功，並且成為超級任天堂平台上最受歡迎的遊戲之一，最終銷售量達到數百萬套。隨著時間的推移，這款作品被認為是系列中最具影響力的作品之一，也奠定許多後來《太空戰士》系列的設計理念。總結來說，這是在劇情、角色發展和遊戲機制方面都達到極高水平的角色扮演遊戲。它不僅將該系列推向更高的高度，也在RPG遊戲的歷史上留下深刻的印記。

Final Fantasy IV is a role-playing game (RPG) developed by Square (then known as Squaresoft) and first released for the Super Nintendo (Super Famicom) in 1991. As the fourth installment in the series, it had a profound impact on the RPG genre and is considered one of the most groundbreaking entries in the Final Fantasy franchise. It made significant advancements in narrative depth, character development, and gameplay mechanics, introducing many innovative elements that influenced later RPGs. The game was later ported to platforms such as the Nintendo DS, mobile devices, and Windows.

The story takes place in a fantasy world governed by the four elements—fire, water, wind, and earth. The protagonist is Cecil Harvey, a dark knight and captain of the Red Wings under the Kingdom of Baron. At the start of the game, Cecil is tasked with retrieving a mysterious artifact known as the Crystal to aid the king’s ambitions. After bombing the village of Mysidia under the king's orders to seize the Crystal, Cecil grows uneasy about the morality of his actions and questions the king’s motives. This leads to his dismissal, and he is sent to the village of Mist with his friend Kain to deliver a mysterious package. Upon arrival, the package releases monsters that destroy the village, leaving only Rydia, a young girl and summoner, as the sole survivor. In her distress, Rydia summons Titan, causing an earthquake that separates Cecil from Kain. This marks the beginning of Cecil and Rydia’s journey to uncover the truth behind the king’s intentions and the Crystals.

As the story unfolds, Cecil experiences inner conflict and eventually chooses to defy the king after discovering that the Crystals are being used to control the world. He is joined by various allies from different backgrounds, including Rosa Farrell, a white mage and archer; Tellah, a legendary sage from Mysidia; and Yang Fang Leiden, a brave martial artist. Each character has their own motivations and backstory, and as the narrative progresses, their relationships and emotional bonds deepen.

Eventually, Cecil and his companions learn that the Crystals are part of a larger conspiracy, with a greater threat looming behind the scenes—a dark sorcerer named Golbez who seeks to reshape the world through the Crystals' power. The game delves into themes of sacrifice, friendship, betrayal, and redemption, which were innovative for RPGs at the time. The story explores destiny and personal choice, making it more than just a simple adventure.

The game world features an overworld, an underground realm inhabited by dwarves, and a moon that becomes accessible later in the game once players acquire an upgraded airship. The ultimate confrontation takes place on this artificial moon, where the final boss and the powerful summon Bahamut await the heroes.

A key turning point in the game occurs when Cecil must confront his dark self in a battle and emerge as a Paladin. Upon this transformation, his level resets to zero, meaning players do not need to excessively grind experience points early in the game. Summons play a crucial role in battles, offering powerful offensive and healing abilities, but they consume a significant amount of MP. Acquiring ultimate black and white magic can accelerate progress through the game.

Final Fantasy IV retains classic series elements while introducing notable innovations and improvements. One of the most significant additions is the Active Time Battle (ATB) system. This system replaces the traditional turn-based combat with a more dynamic, real-time mechanic where each character's action is determined by the filling of their ATB gauge. Once the gauge is full, players can command the character to attack, use magic, or perform other actions. This introduces a sense of urgency and strategy to battles, as players must make quick decisions while managing the flow of combat.

The game’s core commands include:

1. Item – Use healing items or tools.
2. Magic – Cast spells.
3. Equipment – Change gear and weapons.
4. Status – View character stats.
5. Order – Arrange party formation. Mages and summoners are best placed in the back row to avoid heavy attacks.
6. Row – Switch characters between front and back rows.
7. Config – Adjust game settings.
8. Quick Save – Temporarily save progress.
9. Save – Save the game at designated points, usually outside dungeons.

Characters have unique jobs and abilities that align with the story’s progression. Unlike earlier entries, Final Fantasy IV does not allow free job changes; instead, characters' abilities evolve naturally through the plot. This enhances the narrative's focus on character identity and development.

Summons, a new addition to the series, allow players to call forth powerful creatures to aid in battle. Each summon has distinct abilities and can be used strategically based on the situation. While magic is effective, summons are often the most powerful tool in the player’s arsenal, and collecting summons scattered throughout the world is essential to success.

In the game’s early stages, Cecil can use "Darkness," a skill that damages all enemies at the cost of his health. Once he becomes a Paladin, he gains the ability to cast white magic. Kain, his companion, can perform "Jump" attacks, which deal high damage but require charging time. Rydia, as a summoner and black mage, can use offensive spells and summon creatures, though she levels up more slowly.

The game’s world includes towns, dungeons, and various fantastical environments, each offering unique challenges and opportunities for exploration. Hidden treasures, puzzles, and secret enemies populate these areas, encouraging thorough exploration. The dungeon designs balance combat, puzzle-solving, and strategic planning, providing both challenge and excitement.

Upon release, Final Fantasy IV received widespread acclaim for its story, character development, and the introduction of the ATB system. It was praised for advancing storytelling in RPGs, with deeper emotional engagement than previous titles. Nobuo Uematsu’s soundtrack also garnered high praise and remains one of the most iconic game scores in history. However, some criticized the game’s linear structure and the heavy focus on combat, suggesting it lacked freedom in exploration. Despite these criticisms, the overall reception was overwhelmingly positive.

Commercially, the game was a major success, selling millions of copies and becoming one of the most popular titles on the Super Nintendo platform. Over time, Final Fantasy IV has been recognized as one of the most influential entries in the series, laying the foundation for many design concepts in future Final Fantasy games.

In summary, Final Fantasy IV is a landmark in RPG history, excelling in storytelling, character development, and gameplay innovation. It not only elevated the series to new heights but also left a lasting legacy in the genre.