(Ok this is to update some things. Anya was born in Russia (mom died in childbirth) and lived there until she was five, but her dad decided to move to Romania near the Hoia-Baciu forest, where Anya discovered her connection with the bauk (cursed spirits in this case) living in the forest. Her cursed technique is now being able to harness or channel cursed energy from cursed spirits into herself and others. Eventually, her dad began to sense cursed energy coming from Reactor #4 in Chernobyl, so they journeyed to the reactor from Romania, then once her dad was killed (He had reflected Glupyy's cursed energy back at himself, and had died from the intensity of it, but also managed to destroy most of Glupyy's cursed energy. Glupyy found her burning alive, saw her potential, healed her, and put a memory block on her. He was very weak at this point, so the exertion almost destroyed him entirely, but he managed to survive. He took Anya with him to Russia, where he began to train her first how to harness his own cursed energy, and then began to teach her how to harness cursed energy into him from lower level curses. (He was hoping to regain power) She lived there until she started having dreams (memories) of her dad and the Chernobyl reactor (she still has nightmares of burning alive) due to Gluppy's memory wipe wearing off from his proximity to her, so she journeyed to the reactor with Gluppy (who tried to dissuade her) but she went anyway, and regained her memories fully upon her return. She confronted him and he wiped her memories of him and Chernobyl completely, (and most of her training) and disappeared. She then went back to Russia, (she was 12 at this time) where she remained for 3 years until she was recruited to JJK high by a visiting sorcerer from Japan.
(Ok, about her cursed technique... she still has her domain expansion (she doesn't develop it until the Culling Games) and she can summon bauk, but only because she has a special connection and permission with them) When she harnesses a cursed spirit's cursed energy, she also gains some of their abilities, such as hyper-awareness, agility, and cursed energy claws from the bauk (NO NOT THE SAME AS YUKA, IT JUST MEANS SLASHING PUNCHES, NOT LITERAL CLAWS) so yeah that's it. Oh wait no hold on ok so the reason she left Japan before Shibuya was when she decided to follow her nightmares of Chernobyl, which had returned with the presence of Glupyy at the school. Glupyy followed Anya to Russia, as he was losing power rapidly, and needed her to restore him, but didn't realize that his proximity to her was breaking her mental block. Anya goes back to Russia to investigate her dreams, and finds Chernobyl and slightly remembers, but it doesn't fully work this time. During this, she hears about Shibuya and rushes back for the Culling Games, then confronts Glupyy, who restores her memories completely. She is livid that she trusted him, and maxes out her cursed energy output. Glupyy realizes that she will likely exorcize him, and uses the last of his energy to revert to his final form in order to kill her, knowing that they will both be reincarnated in a thousand years even if he loses. He uses all of his cursed energy in a final blast to kill her, (same one that killed her dad) But she creates a successful domain expansion at the last second after she remembers her dad. (She has a moment with a ghostly vision flashback sort of thing) Anya kills him in the domain by channeling his cursed energy into herself and into her bauk, which forces him to revert to his weakened form. He says that even though she has defeated him now, they will both be reincarnated in a thousand years. She states that even her reincarnation would never think to help him again, and sets her bauk on him, who tear him apart. Afterwards she fights curses aimlessly, as she becomes trapped with other sorcerers in Japan. At the Shinjuku showdown, she fights Sukuna with the others and witnesses many of her classmates and teachers die, which basically destroys her emotionally and mentally. She'll probably also sustain some injuries as well. After the battle is over, she returns to the Hoia-Baciu forest and lives with the bauk) (OH ALSO she began as a second grade, then was promoted to semi-first grade and then first grade)