Magic Knight Rayearth represents acclaimed studio CLAMP's most recognised entry into the science-fiction genre, creating a magical super-robot series in the vein of Aura Battler Dunbine, but with aspects of the fighting magical girl genre popularised by Sailor Moon. Across its two series it gradually moved away from the fantasy adventure aspects and more into the super-robot field, eventually becoming a very standard robot adventure series with themed villains of different specialties and later-revealed overlord and rival figures in Debonair and Nova. Coming as it did at a time when animproducers were seeking to attract new audiences in established genres (around the same time as other mecha series for female audiences, such as Gundam Wing and Brave Command Dagwon, were airing), its first series provided a novel approach to super-robot animthat holds up well today.
The comparatively low-key approach to super-robot animshown by Rayearth series 1 makes it a far more interesting series than the second, which focuses somewhat more on the setting as a whole rather than a single quest, and introduces a large number of one-note villains whose interactions are somewhat predictable. For much of the first series there are no robots at all; the emphasis is far more on the magical girl aspect, and the characters are given a lot of time to shine outside of the action and as an ensemble. A team is built up of three disparate characters, as is common in hero anim , with the quest focusing on evading and defeating a series of lesser villains as part of an extended training sequence culminating in a true final battle against the clearly-defined leading enemy. By contrast, the second series begins some time later with the protagonists called back to protect the fantasy world from invading nations and an evil overlord - there is far less of the interaction since for much of the story the three heroines are separated or in some way unable to interact with each other. The result is a series far heavier on action, with some strong setpieces involving innovative enemy designs, but lacking in the character humour that made the initial episodes so memorable. Series 1 played around with genre-savvy and genre-naive characters interacting, and the ways in which the fantasy world depicted worked against those characters' preconceptions - it was an entertaining rendition of a familiar fish-out-of-water story that had a strong cast both of heroes and villains. Having the mecha aspects of the story be the endpoint of the quest provided an interesting development of the action from at first mundane fantasy combat, through magical girl fighting and finally to robot action that built upon all of the previous aspects - while it was still ultimately an episodic kind of action with gimmick-based monsters sent each episode by themed villains, the development of abilities was justified well within the story.
This kind of unlocking of abilities as a method of character evolution (quite distinct from character development) is the core of a good superhero, magical girl or super-robot story. There are a number of different approaches used to it, but the most interesting - and the one Rayearth uses in its "training" arc - is that the characters receive new powers as "rewards" for maturation or development. An enemy is sent to test the characters and they receive a new power to defeat it after understanding its nature. There is a subtle difference here to the method used by some super-robot stories where new attacks are "unlocked" as needed, or previously worthless weapons become useful against specific foes - most of the climactic, "pinch" battles faced by the protagonists in Rayearth are not defeated specifically by the new move that accompanies them. In a series like the archetypal mecha animGaoGaiGar, a new ability is created or developed during the episode by the protagonist's support team based on the requirements of the fight, in order to prevent defeat. Often this will then prove of only limited use in subsequent episodes, creating a consistent escalation of scale and power which nevertheless never really feels like a proper development but instead a series of disparate enemies with unique weaknesses. Rayearth has its protagonists become more powerful instead by becoming more proficient at using clearly-defined abilities, and expanding the scope of those abilities - the end result is similar (the powerful protagonists use their newly-developed unique abilities to solve a specific problem) but the overall picture is less of a succession of one-shot special weapons and more of a traditional fantasy quest progression. This is even highlighted in the series - Umi is shown to be the most genre- and pop-culture-aware member of the team, and talks about how the story's progression is typical of fantasy fiction.
By contrast, the second series has far less of this sense of progression; there is no journey to make, and instead the city-under-siege plot creates a much more stagnant kind of storytelling. Three villain groups are introduced, each predominantly interact with one of the heroines, and then all team up against the real villain at the conclusion. Here there is more of the robot action and the more traditional special move and countermeasure-focused combat, because the journey of discovery and mastery has occurred. The second series is established as a direct continuation of the first, creating one long story in two halves, and yet is also tonally quite different as necessitated by the changing setting. It is a quite standard super-robot series with the relatable and amusing villains giving way to a more competent one that might be seen in a Yuusha series, but at the same time it felt - to me - like a less interesting series as a result. As the fantasy world broke down, the scope of the setting reduced and the increased emphasis on separating the characters and focusing on their individual interactions with villains, rather than the group set against an enemy and interacting both with each other and with the enemy, led to a lack of the amusing and endearing chemistry that made the original series stand out.