(I'm sure or all of this has been explained somewhere already, but I need an outlet for my KH thoughts.)
Anagrams of Xehanort (without the X): No Heart, Another, No Earth
No Heart and Another are fairly obvious. The Heartless, Xehanorts obsession with manipulating hearts or replacing others' hearts, and making others into "another" of himself all qualify.
No Earth? Well, let's see, what characters' names reference the Earth? Riku's name is the pronunciation of 'land' in Japanese, and Terra is Latin for 'Earth'. What has Xehanort (or some form of Xehanort) done to Riku and Terra? Possessed them, tried to take them over, remains a constant threat to their individuality (though Riku has sense found himself again). Xehanort has attempted numerous times to rid these two characters of themselves and claim them for himself: There would be no Riku or Terra left, hence the anagram "No Earth".
"There are many worlds but they share the same sky. One sky, one destiny."
Sora's name can be interpreted as 'sky' in Japanese. The worlds share the same sky, aka., Sora. Sora is one of the heroes of the series, often the main hero. Sora travels the worlds to save them often enough, as he's done it three times already (and once more if we count data Sora). His destiny is to save the worlds and the people that inhabit them. One Sora, or one hero, with one destiny across all these different worlds.
Let's look at Kairi and Aqua.
Kairi's name can be interpreted as "sea" in Japanese. Aqua is Latin for 'water'. Kairi has been seperated from Riku and Sora, her best friends, quite a few times in this series. Now, if we want to be figurative, we can say that she was seperated from them numerous times by "the sea of worlds". Outer space is often compared to a large and endless ocean, so this is a short stretch. More literally, though, Sora was taken from Kairi at the end of KH 1 as their piece of land broke apart and Sora was forced away from her. Here there is a literal sea between them as they get further apart. We often see Kairi staring out to the sea while at the Destiny Islands. Kairi's theme has become separation from her friends, and a sense of longing for them to all be reunited.
Aqua is very similar, though she has taken a more active role. She wants her friends to be reuinited as well, as she sees plot and schemes manipulating them and straining their friendship. Aqua chases Ventus and Terra to both close the physical distance between them and the social distance created by Xehanort's plans. They close that social distance by the end of BBS, but physically they are torn apart again as Aqua saves Terra and is herself trapped in the Realm of Darkness. A parallel to Kairi, we see (in one of those BBS endings) Aqua meeting the real Ansem and staring out over the sea at the Dark Margin (the same place we say in "Another Side, Another Story"). In fact, this is the same place Sora and Riku were trapped at the end of KH 2 before being reunited with Kairi on the Destiny Islands.
Sora, Ventus, Vanitas
Let us acknowledge for a moment the genius in Nomura choosing the name "Vanitas". One, it is similar sounding to Ventus, so that's good. Two, it is Latin for "vanity" or "emptiness". Three, it uses the same kanji (Japanese letters) for Sora in it, which makes it literally a reference to two characters while giving Vanitas' own character a meaning as well. While Sora is "sky", Vanitas can be seen as "emptiness", though both are similar and entirely different. The sky can be full of things, all inclusive, like Sora and his love for his friends, or it can be empty and lonely, like Vanitas and his reliance only on himself. Even looking at the Unversed, the fact that they come from within Vanitas (and his negative emotions like loneliness and hatred to boot) emphasizes his theme of being alone. Ventus, whose name means 'wind' in Latin, is very similar to Sora in the way he acquires and cares for his friends. He's free flowing, moving from world to world and carrying his friends with him wherever he goes. Roxas, being an anagram of Sora's name, shares this trait for friendship with his counterparts.
So there you have it. Names mean stuff.
Anagrams of Xehanort (without the X): No Heart, Another, No Earth
No Heart and Another are fairly obvious. The Heartless, Xehanorts obsession with manipulating hearts or replacing others' hearts, and making others into "another" of himself all qualify.
No Earth? Well, let's see, what characters' names reference the Earth? Riku's name is the pronunciation of 'land' in Japanese, and Terra is Latin for 'Earth'. What has Xehanort (or some form of Xehanort) done to Riku and Terra? Possessed them, tried to take them over, remains a constant threat to their individuality (though Riku has sense found himself again). Xehanort has attempted numerous times to rid these two characters of themselves and claim them for himself: There would be no Riku or Terra left, hence the anagram "No Earth".
"There are many worlds but they share the same sky. One sky, one destiny."
Sora's name can be interpreted as 'sky' in Japanese. The worlds share the same sky, aka., Sora. Sora is one of the heroes of the series, often the main hero. Sora travels the worlds to save them often enough, as he's done it three times already (and once more if we count data Sora). His destiny is to save the worlds and the people that inhabit them. One Sora, or one hero, with one destiny across all these different worlds.
Let's look at Kairi and Aqua.
Kairi's name can be interpreted as "sea" in Japanese. Aqua is Latin for 'water'. Kairi has been seperated from Riku and Sora, her best friends, quite a few times in this series. Now, if we want to be figurative, we can say that she was seperated from them numerous times by "the sea of worlds". Outer space is often compared to a large and endless ocean, so this is a short stretch. More literally, though, Sora was taken from Kairi at the end of KH 1 as their piece of land broke apart and Sora was forced away from her. Here there is a literal sea between them as they get further apart. We often see Kairi staring out to the sea while at the Destiny Islands. Kairi's theme has become separation from her friends, and a sense of longing for them to all be reunited.
Aqua is very similar, though she has taken a more active role. She wants her friends to be reuinited as well, as she sees plot and schemes manipulating them and straining their friendship. Aqua chases Ventus and Terra to both close the physical distance between them and the social distance created by Xehanort's plans. They close that social distance by the end of BBS, but physically they are torn apart again as Aqua saves Terra and is herself trapped in the Realm of Darkness. A parallel to Kairi, we see (in one of those BBS endings) Aqua meeting the real Ansem and staring out over the sea at the Dark Margin (the same place we say in "Another Side, Another Story"). In fact, this is the same place Sora and Riku were trapped at the end of KH 2 before being reunited with Kairi on the Destiny Islands.
Sora, Ventus, Vanitas
Let us acknowledge for a moment the genius in Nomura choosing the name "Vanitas". One, it is similar sounding to Ventus, so that's good. Two, it is Latin for "vanity" or "emptiness". Three, it uses the same kanji (Japanese letters) for Sora in it, which makes it literally a reference to two characters while giving Vanitas' own character a meaning as well. While Sora is "sky", Vanitas can be seen as "emptiness", though both are similar and entirely different. The sky can be full of things, all inclusive, like Sora and his love for his friends, or it can be empty and lonely, like Vanitas and his reliance only on himself. Even looking at the Unversed, the fact that they come from within Vanitas (and his negative emotions like loneliness and hatred to boot) emphasizes his theme of being alone. Ventus, whose name means 'wind' in Latin, is very similar to Sora in the way he acquires and cares for his friends. He's free flowing, moving from world to world and carrying his friends with him wherever he goes. Roxas, being an anagram of Sora's name, shares this trait for friendship with his counterparts.
So there you have it. Names mean stuff.