There are various platforms where you can find bear x lulu fanfiction. Websites like Archive of Our Own (AO3) might have some. You can search for it using the specific tags 'bear' and 'lulu' on the site. Just be aware of the site's rules and regulations while exploring.
Their relationship could start with curiosity. Lulu, being the curious fae, might be interested in Veigar's dark magic. Veigar, on the other hand, might be intrigued by Lulu's ability to manipulate nature with her magic. This initial curiosity can lead to them spending more time together, gradually understanding each other.
In this fanfiction, Lulu is likely a character who has the task of raising Naruto. She could be from a different realm or have a very different background from the Naruto universe. Maybe she's a sorceress or a wise woman with her own secrets and powers that she imparts to Naruto as he grows up.
Another theme is her relationships, especially with the other characters from Final Fantasy X. For example, her relationship with Wakka is often a central point in some fanfictions, showing their bond and how they support each other.
Perhaps there is a powerful enemy that exists in both universes. Naruto and Lulu, through some magical or chakra - related means, are made aware of each other's existence. They meet and combine their unique powers. Lulu's magic and Naruto's ninjutsu could create some really cool and unexpected combat techniques, like using Lulu's polymorph spell on Naruto to give him a new form with enhanced ninja abilities.
A new villain could be created specifically for this fanfiction. This villain could be a being that feeds on the chaos between the two different universes. It has the ability to disrupt chakra flow in Naruto's world and nullify magic in Lulu's world. Naruto and Lulu would have to figure out how to work together to stop this entity before it destroys both of their homes.
A possible plot could be that there is a magical competition in the League of Legends world. Lulu and Veigar both enter. At first, they see each other as rivals. But during the competition, they face a common enemy who is trying to disrupt the event. They then team up, combining Lulu's whimsical magic and Veigar's dark magic to defeat the foe and in the process, form a unique bond.
In this fanfiction, it could be that there is a prophecy that involves both Lulu and Naruto. The prophecy states that only by combining their powers can they save both their universes from a great evil. So, they meet and at first have communication problems due to their different backgrounds. However, as they train together and share their stories, they form a deep bond and work towards fulfilling the prophecy.