Would a darkness infiltrating Elrena explain a personality change? I also wonder, if two did attach themselves to Riku and Vanitas, what happened to them when their hosts were murdered in cold blood? This series presents so many questions and I love having a series to follow with questions posed - The Leftovers is my favourite TV series of all time and all it is is questions - but with KH I'm desperate for answers.
I have had the same thought with you after this update. Although mine related more afterward during their transition from Human to Nobody. Correct me if I wrong, but we haven't had any clear confirmation or definition about Nobody beside a body without Heart (which related to emotion) will also had a change in their mind (or will, or personality)?
Because beside the only reason that convinced me for someone is shy and introvert like Elrena turned 180 degree into a funny lunatic like Larxene is some traumatic events happened during her post-UX era, or when you growth older you become more "mature". The same goes to Lauriam / Marluxia. For me, emotion and personality (heart and mind) are not related to each other. And to see how Nomura has stated about these human elements for past titles many times, I also believe in this theory. (or not a theory, I don't know, my lack of English understanding)
One point I think would contribute to this topic is how Scala's era and post-Scala where Masters being trained in their mindset is to travel into the sea of world's between with your armor on. Now we know Formless Darkness need a body to survive or they will lost their own will, and Keyblade Master's armor during future days teaching (let's assume that) never explain fully about this concept, but only briefly touch about you will be submerge in darkness. This darkness will control your will, thus linked back to why empty Terra's armor being called Lingering Will; OR when Master Xehanort first time let go of his armor during the travel and submerge into the darkness (this darkness is different from the darkness he met during his youth at Destiny Islands, which is also confusing to identify which one is which) . Terra when combined with Master Xehanort still has his emotion sleep deep inside, or when Ven being controlled by Vanitas's will, his emotion still lives
I hope I didn't make all of you being confused with how I deliver the post. Nomura already cut what a human body have into pieces for story ideas, so why not let this happen?