She's not useless as some think. Even before kh3 she's an important character. I'm just going to start by listing accomplishments
BBS: gave Aqua the Destiny's embrace keychain by giving her the flowers
KH1: Without Kairi the Kingdom Hearts series would most likely not even exist. Kairi is how Sora and Riku found out about other worlds and why they wanted to travel to them. Had she not been there all kh events would'nt happen. She also serves as the main drive for Sora to continue his journey in KH1 and she is the reason Sora was able to recover his somebody form after becoming a heartless.
Com: She once again serves as a drive for Sora to continue through Castle Oblivion until his memories of her become replaced. And Namine ends up using Kairi's form to help Riku control his light and darkness. While this isn't directly Kairi doing anything this shows an impact she has on Riku.
KH Days: Xion greatly resembles Kairi to Roxas because of the fact that sora's memories with Kairi are the strongest.
KH2:
Starting off with this we see yet again that Kairi is important to Sora. And she gets her keyblade in KH2.
Coded: Admittedly she doesn't really do anything in Coded besides giving Sora the letter from Mickey.
KH3D: Besides appearing in The World That Never Was as a figment Kairi also is eluded to being a light in the secret ending.
Keeping all of this in mind she'll most likely also be doing a lot of fighting and usefulness in KH3 as well.
She's not useless as some think. Even before kh3 she's an important character. I'm just going to start by listing accomplishments
BBS: gave Aqua the Destiny's embrace keychain by giving her the flowers
KH1: Without Kairi the Kingdom Hearts series would most likely not even exist. Kairi is how Sora and Riku found out about other worlds and why they wanted to travel to them. Had she not been there all kh events would'nt happen. She also serves as the main drive for Sora to continue his journey in KH1 and she is the reason Sora was able to recover his somebody form after becoming a heartless.
Com: She once again serves as a drive for Sora to continue through Castle Oblivion until his memories of her become replaced. And Namine ends up using Kairi's form to help Riku control his light and darkness. While this isn't directly Kairi doing anything this shows an impact she has on Riku.
KH Days: Xion greatly resembles Kairi to Roxas because of the fact that sora's memories with Kairi are the strongest.
KH2:
Starting off with this we see yet again that Kairi is important to Sora. And she gets her keyblade in KH2.
Coded: Admittedly she doesn't really do anything in Coded besides giving Sora the letter from Mickey.
KH3D: Besides appearing in The World That Never Was as a figment Kairi also is eluded to being a light in the secret ending.
Keeping all of this in mind she'll most likely also be doing a lot of fighting and usefulness in KH3 as well.