I don't get this...

[Shinra]

I'm wondering... if any of you know what happens to Aqua when she goes through this moment in the final Terranort fight...
YouTube - KH birth By Sleep Final Episode Final Boss English Kingdom hearts BBS Walkthrough Part 54 PSP

Refer to moment 6:43-6:54...

It looks like a moment that Terra and Aqua work together to achieve something... I'm just not sure what. To get her back into the fight perhaps, to possibly free Terra's heart or something?

 

[Vani]

i think its something about terranort sucking aqua into his heart and terra helping her fight him for a bit on the inside as well as get her out. or something.

 

[Spire]

They're using the Trinity Limit move together (this is the same one you can buy in Mirage Arena for 1400 medals for use in multi-player). Although, the reaction command says "Dual Limit" in the video because there's only 2 of them performing the move.

i think its something about terranort sucking aqua into his heart and terra helping her fight him for a bit on the inside as well as get her out. or something.

Yeah, something like that... Nomura never clarified as far as I know.

 

[Absent axel]

Well it happened 3 times after i healed myself literally right in front of terranort so maybe its connected to healing, other then that i like the fact that you can either attack terra or dual limit with him XD

 

[Zulkir]

Nope, it happens when the Guardian grabs you and you successfully mash X instead of getting combo'ed by Terranort. You go into his heart and help Terra defeat some darkness orb. If you succeed it actually does quite a bit of damage to Terranort.



And this is spoiler-filled, should be put in the spoilers section.

The overwhelming majority of topics in the BBS section are better suited for the spoiler section to be honest.

 

[Th Key of Destny]

SPOILERS, but then again so is this whole question and all the answers.
Yea if you manage to dodge the guardian and get to Terranort himself without actually hitting him before hand, and tap square when you enter the field on the ground you will be prompted to use the dual limit command, and for that very brief instant you see Terranort as the actual Terra.
Kinda cool, like you're helping Terra fight for control over his heart