When Cloud and Tifa met at the well in Nibelheim, their conversation went a little bit differently. Cloud told Tifa his desire to leave town and join SOLDIER, to become more like his Hero, Sephiroth. Tifa made him promise to come rescue her if she was ever in trouble, and he agreed. After a moment, Tifa amended the promise to "And if you're ever in trouble, I'll come help, too, ok?" And so their promise was made.

A week later, when Cloud was about to leave, he suffered an accident and broke his arm and leg. In addition to being laid up for a while, the doctors suggested that he may suffer lasting trauma to both arm and leg, and possibly perpetual numbness in his etremities, so Tifa went to see him and told him that she would make his dream come true. As a result, she swore she would go in his place and make everyone proud. She promised she would become famous one day, so he could see her in the papers, and then she would come back a hero. Cloud didn't have much of a choice as the recruitment in Costa del Sol was almost over for the year, and with mixed feelings reluctantly agreed. She left Nibelheim to join SOLDIER.

Her family life had never been the same since her mother died, and her father seemed to grow both more distant and overprotective of her. While she loved her father, the over-protectiveness seemed to grow more and more oppressive as time passed, and so it was easier to decide to follow Cloud's dream when he had his accident. When she told her father her plans to leave, he protested and they argued, though in the end she left anyway while he was out, leaving only a note. She had to find her own path.

The entry requirements to SOLDIER strict, and Tifa had to lie about her age in order to get in by one year. Driven by her desire to make Cloud's dream come true, she persevered and made it through the first few trials. At this point she had a few setbacks due to her gender.

Many male candidates made fun of her and the other female candidates, and mocked her for thinking she could get into SOLDIER. This had the effect of making her more determined- after all, she wasn't doing this just for herself, but for Cloud as well. This strengthened her will and body in the long run, and she grew a thicker hide and a stubborn streak. When the next requirement tests came up she passed with flying colors, leaving the other candidates in her dust.

As a part of the process, she was subjected to Mako showers and Jenova augmentation. This proved to be a bit of an ordeal for her, taxing her mentally and physically with the strain of not knowing quite what was happening to her. She finally achieved the rank of SOLDER 3rd class when she was 15, and carried enough scars to prove it.

It wasn't very long after she had made it to 3rd class when she was assigned to a contingent consisting of Zack Fair, Sephiroth, and several regular militia. She had met Zack before and worked with him on some minor missions, and was excited at the chance to work with Sephiroth himself as well, though she generally hung out with Zack during the long trek to Nibelheim, and shared her disappointment she hadn't made 1st before going back home. Zack reassured her that she had gotten this far, and that was something to be proud of.

When they got to Nibelheim, Tifa was surprised to discover Cloud would be guiding them through the mountains. Apparently he had decided to wander the mountains fighting monsters in order to become stronger and join Tifa in SOLDIER, as he was learning to live with the occasional numbness. Feeling slightly ashamed and not wishing to make Cloud feel bad, Tifa decided to hide her identity from him for the time being, though she went to visit her father while she was in town.

Unfortunately, her reunion with her father wasn't marked any happier than their parting, as they quickly got into an argument about her life choices and having left the way she did. She left fairly soon after visiting, feeling upset and like there was a permanent rift between them now.

When they finally headed out to the reactor, Sephiroth discovered the Jenova Project and subsequently proceeded to the library in the basement of the Shinra mansion and read everything he could on the subject. Meanwhile, Tifa and Zack hung about town, worrying about Sephiroth and his odd behavior, Zack moreso than Tifa as he knew Sephiroth longer. Days passed, and the contingent got restless, until Sephiroth finally emerged from the basement, and burned Nibelheim down.

Tifa's father ran after Sephiroth, Tifa ran after her father. Cloud and Zack weren't far behind. Tifa arrived at the reactor just in time to see Sephiroth cut down her father, and head into the central chamber. Tifa screamed and flew into a berserk rage. Everything she had known was gone, and she hated Shinra, for what they had done to her, to Sephiroth, to her hometown and for creating mako reactors, and worst of all- taking her father away when their last words together had been in anger.

Zack and Cloud arrived, and Cloud tended to Tifa's father while Zack and Tifa ran after Sephiroth to stop him. They both fell to the Masamune. After retrieving the Buster sword from Zack, Cloud ran after Sephiroth and confronted him, hitting him with the Buster sword and in turn getting the Masamune in the gut. As a last act, Cloud tossed Sephiroth into the mako lake below them.

During the aftermath, Shinra arrived and cleaned up Nibelheim. Hojo ordered Cloud, Tifa, and Zack to be part of the new Nibelheim experiment, placing them in mako tanks.

After four years, Zack gained enough strength to break free and release Tifa and Cloud. Tifa regained consciousness quickly, but Cloud was another story. His psyche had been shattered, and unwilling to leave him behind, Tifa and Zack took turns carrying him on their way to escape.

They made it as far as Midgar before the Shinra army caught up with them. Zack told Tifa to take Cloud while he held them off, and said he would join up with them later. That was the last Tifa had ever seen of Zack, not knowing if he died or survived. Needing some place to stay, and having a burning hatred for Shinra and all things tied to Shinra, she discovered and joined a small terrorist group called AVALANCHE as a mercenary and a place to allow Cloud to recover.

By now he had regained consciousness, but seemed strange and off. He would say things that didn't make sense, and Tifa's worry grew even as he recovered enough to help out with the group's activities. He seemed to think he was a SOLDIER, and despite Tifa's misgivings she didn't correct him.

Throughout her time with AVALANCHE keeping Cloud alive and happy was her first priority, and taking revenge on Shinra for the Nibelheim incident and the loss of Zack was second. Those became her motivations, her hatred for Shinra and all things the fuel to her fire.