Protip for all you scumbags out there: Even the nicest people in the history of ever probably won't take kindly to you leveling the planet twice in the same damn century.
Ok, just a little side note here: If Celica A. Motherfucking Mercury thinks you're too much, there is no hope of redemption for you whatsoever. Celica's got a lot of forgiveness in her, and she's made friends with quite a number of people who others would want nothing to do with (and for good reason). But even putting aside what Terumi's done to her personally (Killing her sister and best friend, taking said sister's soul after he killed her and turned her into a mind-controlled puppet, fucking up her other best friend/crush so bad and basically ruining his life, killing her (sort of), the list goes on for decades), the scale of his crimes and acts of douchebaggery are just so off the fucking charts that even she's got the memo that he's got no humanity in him, period.
Celica thought they were finished with him for good after Hakumen killed him back in their world, but those wacky scientists seem to get a hard on for bringing in people who enjoy making others miserable, and now he's here in Hive City along with them. Quite frankly, Terumi's presence scares her far more then anyone or anything else in the Hive. She's seen firsthand the scale of mass destruction he's capable of of working with. As far as she's concerned, he is currently the biggest threat in Hive City. And considering his track record, she's probably not too far off.
So now, she's gonna do everything in her power to take him down once and for all. Celica doesn't care what kind of reputation he gets, what kind of allies he has, or what plans he has for the city. She's sick and tired of seeing Terumi hurt people, and she's not gonna stand for it anymore. Hopefully, with the other BlazBlues and friends she's made here in the Hive, she'll be able to help out enough to stop him in his tracks.
tl;dr: Got so close, got so far, only to get killed be his loli ex-girlfriend and a brother obsessed power ranger. Congratulations, and my condolences. Except not really. He fucking deserved it.