If we assume 'in live' means 'involved', Naruto can be involved with fanfiction through the creativity of fans. Fans write stories about him, so he becomes part of the fan - created fictional scenarios.
There's also 'Date A Live: Ninja Invasion'. This fanfic has a really cool concept where the ninjas from Naruto start to show up in the Date A Live world, causing chaos and also creating some unexpected alliances. It's full of action and some really fun character interactions.
It could mean that Naruto, the character from the Naruto series, is somehow involved or associated with fan - created fictional works in an interesting way. Maybe it implies that there are fanfictions that are very much centered around Naruto's character and his storylines.
It could mean that in the Naruto universe or among Naruto fans, someone named Naruto (or a character representing Naruto) destroyed a fan - created fictional work that was still ongoing or 'live'. Maybe it was a fanfic that violated some unspoken rules or ethics within the fan community.
One common theme is friendship. Just like in Naruto where the characters form strong bonds with their comrades, in Love Live the girls also have deep friendships. In fanfics, these two groups often come together and form new friendships based on mutual understanding and support.
Common themes in 'Live Life Again Naruto Fanfic' include the exploration of 'what if' scenarios. For example, what if a character had made a different choice at a crucial moment? Another theme is the power of knowledge. Characters use what they know from their previous life to gain an edge in the new one. This could be as simple as knowing the weaknesses of an enemy or as complex as understanding the political undercurrents in the ninja villages and using that knowledge to make positive changes. There's also a sense of gratitude and making the most of the second chance at life, which often leads to characters being more proactive in their actions and relationships.
The loyalty aspect. In Naruto, loyalty is a huge theme. When a fanfiction has a character saying 'I live for you', it intensifies that loyalty factor, which is really attractive to fans.
The storylines could be combined by having a character from Naruto end up in the Date A Live world by accident. For example, Naruto could be on a mission and get sucked into a strange portal that leads him to the Date A Live universe. There, he could start interacting with the Date A Live characters, and his presence would disrupt the normal order of things. The Date A Live characters would have to figure out what to do with this strange ninja, and Naruto would have to adapt to this new world with its own set of rules and threats.
In a Naruto x Date A Live fanfiction, a great crossover would be in terms of combat strategies. The Date A Live characters are used to dealing with spirits in their own ways, but Naruto characters bring in a whole new level of combat knowledge. The Date A Live crew could learn about teamwork from Naruto's team formations. Also, the different elemental jutsus from Naruto could be incorporated into the Date A Live world, like using fire jutsu to fight against a particularly powerful spirit.