Ethan and Jessy will meet at age 7, Ethan was a bully because he was angry about his relationship with his dad and felt he needed to feel powerful. He began victimizing all his classmates, especially Jessy. Pulling on her hair and stuff like that, eventually she got sick of it and broke his nose. they hated eachother for a bit after that, but he eventually came to respect her.
Jessy had a very laid back father that wasn't too invasive towards his daughter, which she was very much okay with, liking her privacy. He wasn't the classy type, working at home with his laptop on a well-paying Google job and always chilled. He'd occasionally get out of the house to go to the groceries or spend some time drinking at the pub, but was able to control his addictions' for Jess' sake. He loved her and she loved him, they weren't too picky and left each other just enough space, but still spending some quality time together watching old half-assed movies because they liked it.
As the two grew fond of each other, they were inseparably best friends by the age of 8. They started hanging out with one another more and more until their bonds were secluded from the rest of the world. Ethan liked to spend the night out at Jess' place, seeking refuge from his father. They'd always have sleepovers, and even slept in the same bed before they became teens; during that time, Ethan would let his guard down and so would Emma, as he confessed his fathers' sins while she comforted him. At those moment, they knew they'd always need each other.
Age 13... The two get picked up by the wolves, getting their butts saved on their first monster attack. They train and develop their demigod abilities with Lupa, and were doing just fine until the goddess told them they'd have to go to Camp. Emma, not wanting to leave her father, immediately refused and Ethan shared her fate in order to not get separated. They go back to their home town and manage to disintegrate any monster threat they'd face for a solid year.
Moving on, when Ethan's like 14. He has serious anger issues, ends up joining a gang and just raises all hell. I imagine Jessy tried to talk him out of that stuff, but nah. So eventually Ethan's atrocities caught up with him and had to spend a few years in Juvie.
Since Ethan is taken away from Emma, she decided to go back to Lupa and get into CJ afterwards. Since she was believed to be undisciplined by leaving the training and going back home, she had to prove herself to be worthy of the title of Legionar by fighting one of the wolves one on one, using nothing but a sword, without any armor. Fortunately, she succeeded, but it left various scars on her back as well as in her memories, as it reminded her that she had to face all of this without her best friend. She eventually joined the 5th cohort, having no letters of recommendation from a proper Roman.
The two stay on separate paths until they both turned 17. Ethan was released from juvy and immediately went out to look for Emma, finding nothing but her father, who told her she got a scholarship to some boarding school named "SPQR". He goes to find Lupa once again after 3 years, trains as if he were a new recruit and joined CJ.