I'm not sure who Kane and Katelyn Brown are specifically. But generally, a love story might start with them meeting by chance. Maybe they were at a local event or through mutual friends. They could have been attracted to each other at first sight. Their love then grew as they spent more time together, getting to know each other's likes and dislikes, dreams and fears. And over time, they became a couple, sharing their lives and creating memories together.
Ruin would be a great character to pair with Kane. They both have strong military backgrounds and skills. Their combined combat abilities could make for some really intense and exciting scenes in a fanfiction. They could be on a mission together and use their different specialties to overcome obstacles.
There is no actual 'real story' in a literal sense for Kane and Abel. But in the fictional narrative, Kane is born into a wealthy family and has all the privileges that come with it. Abel, on the other hand, is from a poor background and has to struggle hard. Their upbringing makes a huge difference in their outlooks and approaches to life. Kane is used to getting what he wants easily, while Abel has to fight for every little thing.
Yes, there might be. The Naruto fandom is huge and there are all kinds of fanfictions out there. Some fans might have created a fanfiction where Naruto is a Kane fan. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own.