The KH fandom is no stranger to Kairi hate. In fact, a good chunk of the fanbase embraces the hatred. I'm not one of them, partly because I rarely participate in character bashing, and partly because the Kairi hate can get positively vicious, which really weakens the arguments against her. Still, I can't deny that Kairi is very underdeveloped, especially when you compare her to the other characters. There are many reasons for why she doesn't really deliver as a character, the reasons usually drowned out by the haters' cries of "Kairi sux and blah blah blah."
I'm not a Kairi fan, but on a meta perspective, I feel sorry for how frequently she's bashed (same with Xion). The haters tend to equate her poor role in the story with being a poor character, which isn't quite true. So, here are my own observations for why Kairi gets the short end of the stick, which I'll hopefully try to keep as neutral and analytical as possible.
First, I need to clarify the difference between who a character is, and what a character is. Who a character is is their personality, their motives, their demeanor, etc. What a character is is their role in the story, and what purpose they serve. The what can be a keyblade master, the villain, the king of Disney town, the mentor, the Nobody of the protagonist, etc. In other words, who and what are, respectively, internal and external traits to the character. You can think of the two as the raw, base character personality, and what the story does to and for that character. These two things will (or should) reflect and enhance each other, but they're not one and the same. When the two don't mesh is when problems arise.
Who Kairi is is the sweet, spunky, brave, and caring girl. What Kairi is, unfortunately, is not the best way to convey that who. Kairi is often decried as useless because she can't fight, but while Namine proves non-combatants have their place in KH, she also seems to be the exception rather than the rule. KH is an action series, so the narrative will favor combatants, keyblade wielders above all. The what serves to help convey the who, but if the what isn't done right, the who becomes less relevant.
Let's apply this concept to the other characters: for Sora, the who is a friendly, adventurous, understanding kid without many ambitions. What he is is the protagonist, a special keyblade wielder, the hero, and a fighter. The fighting part is important, because Sora's combat ability and status as a keyblade wielder allows him to demonstrate his caring, heroic personality in a way that befits KH's action-oriented atmosphere. His who and what mesh, and he's a compelling character for it.
For another example of how the who and what mesh, reflect, and enhance each other, let's look at Riku. Riku's who in KH1 is a bold, ambitious, cocky and confident guy who pushes his limits. This fits well with his what, a rival-turned-evil would-be keyblade wielder, Maleficent and Ansem SoD's pawn, and a fighter who is more than a match for Sora. KH's story affects Riku, and Riku affects KH's story, like a good character should. He's compelling because his who and what--or, his character and the story--play upon each other. It carries over into KH2 and beyond, during his battle over the darkness in his heart. His new who (realizes his mistakes, has cooled down significantly, but is still determined enough to fight for salvation) continues to mesh with his what (a person tainted with darkness, for a time had no one but Mickey to rely on, and later on, a powerful keyblade wielder). Riku earned a keyblade because of who he is, and the keyblade, in turn, allows him to actively demonstrate his personality and regained confidence within KH's narrative. There are more whos and whats than that for Riku, but that just shows how strong a character he is.
Now, Kairi? Kairi's what is a poor one, and does not do her who much justice. Kairi's what is supposed to be a normal girl, Sora's crush (shove it, SoRiku fangirls), and someone who can't fight. As KH is an action series, non-combatants are at a severe disadvantage when it comes to being active. Fighting is a major requirement to actively affect the plot in KH. But wait! Kairi is also a Princess of Heart! Except the perks of being a PoH can't be consciously controlled, so it's more a plot device than something that's a part of one's character.
Nomura could've made the PoH thing something beyond a plot device, but he didn't. As Kairi is a normal girl, with powers she can't actively or consciously control, her what is ill-suited for her who. Her what means she gets few chances to demonstrate her who in KH's narrative, and when she does, it's minor in comparison to the feats of Sora and co. The way she's been handled in the story means she's unable to be a compelling character. At least, that's how it was until she got a keyblade.
The way she's been written in the story means it's unreasonable for her to be an active part of things, and that's a complete reflection of her what. It's why people criticize her for not being able to fight. But, now that Kairi has a keyblade and is being trained to use it, she should hopefully become active in things. Her what has changed to include "keyblade wielder" and "fighter," which will allow her to actively move the plot in a way she couldn't when her what was just "normal girl," "Sora's crush," or "Princess of Heart."
It's why people are so optimistic about where Kairi can go. She finally has the chance to actively affect things because KH's narrative can finally accommodate her. Maybe her what can finally become a proper medium to convey her who, that being a sweet, courageous girl who wants to help how she can. And maybe then, people will finally give the poor girl a break, but this being the KH fandom, I'm not getting my hopes up.
The KH fandom is no stranger to Kairi hate. In fact, a good chunk of the fanbase embraces the hatred. I'm not one of them, partly because I rarely participate in character bashing, and partly because the Kairi hate can get positively vicious, which really weakens the arguments against her. Still, I can't deny that Kairi is very underdeveloped, especially when you compare her to the other characters. There are many reasons for why she doesn't really deliver as a character, the reasons usually drowned out by the haters' cries of "Kairi sux and blah blah blah."
I'm not a Kairi fan, but on a meta perspective, I feel sorry for how frequently she's bashed (same with Xion). The haters tend to equate her poor role in the story with being a poor character, which isn't quite true. So, here are my own observations for why Kairi gets the short end of the stick, which I'll hopefully try to keep as neutral and analytical as possible.
First, I need to clarify the difference between who a character is, and what a character is. Who a character is is their personality, their motives, their demeanor, etc. What a character is is their role in the story, and what purpose they serve. The what can be a keyblade master, the villain, the king of Disney town, the mentor, the Nobody of the protagonist, etc. In other words, who and what are, respectively, internal and external traits to the character. You can think of the two as the raw, base character personality, and what the story does to and for that character. These two things will (or should) reflect and enhance each other, but they're not one and the same. When the two don't mesh is when problems arise.
Who Kairi is is the sweet, spunky, brave, and caring girl. What Kairi is, unfortunately, is not the best way to convey that who. Kairi is often decried as useless because she can't fight, but while Namine proves non-combatants have their place in KH, she also seems to be the exception rather than the rule. KH is an action series, so the narrative will favor combatants, keyblade wielders above all. The what serves to help convey the who, but if the what isn't done right, the who becomes less relevant.
Let's apply this concept to the other characters: for Sora, the who is a friendly, adventurous, understanding kid without many ambitions. What he is is the protagonist, a special keyblade wielder, the hero, and a fighter. The fighting part is important, because Sora's combat ability and status as a keyblade wielder allows him to demonstrate his caring, heroic personality in a way that befits KH's action-oriented atmosphere. His who and what mesh, and he's a compelling character for it.
For another example of how the who and what mesh, reflect, and enhance each other, let's look at Riku. Riku's who in KH1 is a bold, ambitious, cocky and confident guy who pushes his limits. This fits well with his what, a rival-turned-evil would-be keyblade wielder, Maleficent and Ansem SoD's pawn, and a fighter who is more than a match for Sora. KH's story affects Riku, and Riku affects KH's story, like a good character should. He's compelling because his who and what--or, his character and the story--play upon each other. It carries over into KH2 and beyond, during his battle over the darkness in his heart. His new who (realizes his mistakes, has cooled down significantly, but is still determined enough to fight for salvation) continues to mesh with his what (a person tainted with darkness, for a time had no one but Mickey to rely on, and later on, a powerful keyblade wielder). Riku earned a keyblade because of who he is, and the keyblade, in turn, allows him to actively demonstrate his personality and regained confidence within KH's narrative. There are more whos and whats than that for Riku, but that just shows how strong a character he is.
Now, Kairi? Kairi's what is a poor one, and does not do her who much justice. Kairi's what is supposed to be a normal girl, Sora's crush (shove it, SoRiku fangirls), and someone who can't fight. As KH is an action series, non-combatants are at a severe disadvantage when it comes to being active. Fighting is a major requirement to actively affect the plot in KH. But wait! Kairi is also a Princess of Heart! Except the perks of being a PoH can't be consciously controlled, so it's more a plot device than something that's a part of one's character.
Nomura could've made the PoH thing something beyond a plot device, but he didn't. As Kairi is a normal girl, with powers she can't actively or consciously control, her what is ill-suited for her who. Her what means she gets few chances to demonstrate her who in KH's narrative, and when she does, it's minor in comparison to the feats of Sora and co. The way she's been handled in the story means she's unable to be a compelling character. At least, that's how it was until she got a keyblade.
The way she's been written in the story means it's unreasonable for her to be an active part of things, and that's a complete reflection of her what. It's why people criticize her for not being able to fight. But, now that Kairi has a keyblade and is being trained to use it, she should hopefully become active in things. Her what has changed to include "keyblade wielder" and "fighter," which will allow her to actively move the plot in a way she couldn't when her what was just "normal girl," "Sora's crush," or "Princess of Heart."
It's why people are so optimistic about where Kairi can go. She finally has the chance to actively affect things because KH's narrative can finally accommodate her. Maybe her what can finally become a proper medium to convey her who, that being a sweet, courageous girl who wants to help how she can. And maybe then, people will finally give the poor girl a break, but this being the KH fandom, I'm not getting my hopes up.