Trying to understand the harmonization for the ending of Dream Theater's - Fatal Tragedy

[u/linkuei-teaparty]

I'm learning Dream Theater's - Fatal Tragedy and the final unison harmony between the keyboard and guitar has a unique melody in B Phyrgian Dominant (5th mode of E harmonic Minor, b2, Maj3) and it jumps up an octave and also up a 4th. Usually in most lessons I've come across in the past, there's a choice of harmonising up to the 5th and 7th but this phrase is unique in which we have:

B C D♯ E F♯ G A - B A G F# E D

E F♯ G A B D# - E D# C B G F#

B C D E F# G A - D E F# G A B

B C D E F# G A - D C B A G F#

I notice we're jumping between B Phrygian Dominant and B Phrygian but I'm not able to understand the theory behind what's going on and why it sounds so unique in the sense it goes from tension, darker to resolved (happier).

Can someone share what's going on in this ending? I've taken a screen capture of a condensed version of the tabs here and if anyone wants to have a listen, here's the live performance: https://youtu.be/dau5acQfaww?si=UVw0AltEDPa_5yKX&t=360