CHRIST okay, I’m going to assume it’s an even playing field, which means either 1) they’re toying with each other, or 2) it’s somehow come down to saving Usagi or saving Haruka (so they’re going all out).

Option 1 probably goes to Mina. Both of them can get very serious even with low stakes, but Mina has that Venus drilling– how you practice is how you’ll fight for real. Michiru has enough of a disconnect from the old Neptune that that’s not present for her. 

Option 2 ends in a draw– mutual destruction. Mina/Venus lives for Usagi/Serenity. Her literal life’s purpose is to keep her alive. Whatever she feels about it, it’s all she has. Maybe she’ll hate herself for the means she choses to reach that end (she will, oh she will), but that end must be reached. 

But Haruka is every good thing for Michiru, the one thing she’s chosen in this whole mess of a life. If it’s Haruka or the world, she’ll choose Haruka– but then, neither of them are really fighting for the world. If Usagi will save it, well, that’s a nice coincidence that bears no effect on Mina’s choice.

They’ll fight like hell until one of them–probably Mina– decides that the way to end it is by having there be only one person left to save. But once Haruka’s dead, there’s no way anyone’s coming out alive. Mina spends the last few seconds of her life hating herself.