Been super busy so I only just now had time to catch up, I actually think Terra telling Riku to keep it secret when he was little fits really well. Look at Riku's talk in KH1
Kairi: So say you get to another world what would you do there?
Riku: Well, I...hadn't really thought about it. It's just... I've always wondered why we're here on this island. If there are any other worlds out there, why did we end up on this one? And suppose there are other worlds... Then ours is just a little piece of something much greater. So we could've just as easily ended up somewhere else, right?
Sora: I dunno
Riku: Exactly. That's why we need to go out there and find out. Just sitting here won't change a thing. It's the same old stuff. So let's go.
This all just works so well with this scene. Riku is still immature at the time, still has no concept that Terra's promise has nothing to do with him getting a keyblade or not. So when Kairi asks him what he do there he can't say "I will go hunt down a mysterious man who had me hold his giant key for a bit in hopes I can get the power to protect you guys". Thus we've got the awkward stuttering, the bs answer that really sounds like Riku is making up everything he is saying right now up on the spot. And the weariness in his voice as if he's been waiting for something and he's finally sick of waiting, in this case now being contextualized as the keyblade. He doesn't know it's name or what it is just that one day he'd get one and be free to leave the island and yet that day never seemed to come. Then we have this part...
Kairi: You've been thinking a lot lately, haven't you?
Riku: Thanks to you. If you hadn't come here, I probably would've never thought of any of this. Kairi, thanks.
"Probably" is there in his sentence implying that there IS another reason he thought of all this. I think this was meant to be one of the MANY subtle hints (well okay some are really on the nose) in KH1 that Riku had met with and talked to the brown cloaked Ansem. But now it's being retconned to Terra which frankly is a retcon I'm okay with because it fits better. Likewise Kairi did still inspire Riku in that as far as he can tell Kairi has no special abilities, no giant key, etc... but she managed to travel from another world. This leads him to think he doesn't need any of that, he doesn't need to wait any longer. It leads him to believe that childish notion that a raft would be able to let him escape the world like Kairi.
I'm like 90% is Dark Impulse's hand is a based on Lingering Will's keyblade gear punch attack. Except LW uses just his keyblade to do it while Terra uses his keyblade and the power of darkness to give it more oomph, it has the same gear spinning effect around it which is one of the only times we see Terra with that. (His delayed keyblade summoning animation is the other time)
Eraqus doesn't really change his gears that much, like an angry parent he got caught up the in the rage and let it cloud his common sense. However he blames everything he did on darkness both Terra's and his own instead of acknowledging that it's his zealous belief in light that did this. Finally this is a very real portrayal of an abusive and emotionally manipulative parent, which is what Eraqus is. The classic "get mad, beat on child, and then apologize as if that makes it better without actually learning anything". Eraqus was a garbage parent from start to finish and I loved it.