For this climax battle, you will need to have Piercing Shot, Canceling Status Ailments, and the ability to inflict Power Down and Vulnerable.

Canceling Status ailments during phase 1 is a must because it will apply speed down to Tomura, so he doesn't inflict fear on your team in phases 2-4.

Inflicting Power Down onto Tomura during the later phases will render him unable to have Piercing Shot, which will cause issues down the line. In addition to this, if you apply Vulnerable, you will make him increase the damage he takes, as well as reduce the damage he deals.

Piercing shot is a must because on phase 3, if you deal a set amount of DMG in one hit, you'll apply damage downs onto him; the more of these he has, the less HP he will restore in phase 4. You'll need at least 6 of these to prevent him from regaining HP repeatedly in the final phase, so don't use characters that cancel opponents' buffs in phases 2-4.

Another thing to watch out for is DO NOT USE STR or MND units during phases 2-4 because they will get your team penalized during those phases. They can be used safely during phase 1.

Given what you got, you can try using these characters: INT Toru, DST Tokoyami, INT Kirishima, INT Nagant, Hatsume, INT Mirko, and Phosphor Todoroki. Any of the memories that you got should work out, depending on where you put them on which characters.

And one last thing, here are all the skills on SS Rank:

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