Missing Hyper Boss

[Shintetsuken]

For some reason, I am missing the Savior Gundam Hyper Boss.

I have S ranked the mission where you get to choose to join the Archangel's crew (twice, once with each option), but I am still not unlocking this boss. I did a quick second playthrough as ZAFT and chose to join Archangel instead of sticking with ZAFT this time: no luck.

I can't find any information about how to unlock this, other than a couple Japanese message board posts of people running into the same problem.

Does anybody know what unlocks this mission? I've beaten all of the other Hyper Boss missions (other than the final one that unlocks when the rest are beaten), and it's driving me insane, as this is the only thing in the way of my Platinum.

Thank you!

[Shintetsuken]

So, I ended up resolving this on my own:
You have to clear it with an S rank on your ZAFT playthrough that does NOT branch off into Archangel route (you can't just play it with SFreedom METEOR and replay the level with the other route on that file, it won't unlock).

My S-rank score was 84782, using Heine's Destiny Gundam. I did not get shot down, saved Heine, and shot down everything except the Chaos Gundam, the Freedom Gundam, and only got one of the two ships (the CPU got the other one), and it was enough.

Good luck to anyone else struggling!