Conversation between DiZ and Riku:
Along with DiZ literally mentioning Roxas' heart there is also the fact that Roxas has emotions.
I'm sure you are saying "plenty of Nobodies show emotion, but they are just lying", but you're wrong!
After Roxas was united with Sora and was no longer an active force, Roxas' fear and sorrow of leaving Twilight Town and his 'friends' made Sora cry.
How could this happen?
But, you are suggesting that Sora and Roxas were sharing a heart when they were two entities. Like when Vexen was attempting to tell Sora about the 'other side' of his heart, in Chain of Memories. One half for Sora and one half for Roxas.
Wouldn't that also mean that Roxas has a heart?
I do not see what we are arguing over anymore.