One idea could be Naruto being adopted by a League of Legends champion from Ionia, like Karma. She could teach Naruto about the spiritual balance in Ionia, which is somewhat similar to the chakra balance in Naruto's world. And Naruto could bring his ninja skills to help protect Ionia from threats.
One idea could be to have Naruto characters possess the powers of League of Legends champions. For example, Naruto could have the power of Jinx's rockets for his Rasengan. Another idea is to create a tournament in the Naruto world where ninjas compete using League of Legends - like skills.
One plot idea could be Vi getting involved in a mystery within the undercity. Maybe she discovers a new, dangerous criminal organization and has to use her skills to take them down. Along the way, she could form an unexpected alliance with an old enemy.
Well, one plot could be that fem Naruto is adopted by a group of wandering ninjas. They teach her unique and unorthodox ninja skills. She then uses these skills to help her when she finally returns to Konoha and has to prove herself to the skeptical villagers.
One idea could be a story where the characters from Naruto are transported to a different dimension within the League of Shadows' realm and have to fight new and unknown enemies. They could form unexpected alliances with some of the League of Shadows' members who have a change of heart.
A possible plot is that a powerful enemy from the future in the Legends of Tomorrow timeline discovers the power of chakra in the Naruto universe. So, they travel back in time to try and harness it for their own evil purposes. The Naruto characters, along with the Legends of Tomorrow crew, must then join forces to stop this enemy. This would involve the Legends of Tomorrow team learning about ninjutsu and the Naruto characters learning about time - travel technology.
Well, his chakra would be seen as a very unique form of energy in the League of Legends world. His Rasengan could potentially be enhanced by the magic - rich environment. For example, if he was in a place like Demacia, the magical runes there might interact with his chakra, making the Rasengan more powerful or having additional effects like stunning enemies.
Maybe the OC is a skilled swordsman from a small, unknown village. He enters a grand tournament in Demacia. There, he catches the eyes of female champions such as Fiora and Lux. Fiora is impressed by his unorthodox sword fighting style, while Lux is drawn to his humble origins. As the story progresses, they all get involved in a mystery that is tied to an ancient evil in the League of Legends world, and the OC's harem grows as more female characters get involved in solving the mystery.
Another plot could be that Naruto is adopted by an older ninja who has retired from active duty. This ninja has a lot of wisdom and secrets. Under his guidance, Naruto discovers a new power within himself that was hidden all along.
One idea could be that Naruto is adopted by a powerful but reclusive shinobi. This shinobi could teach Naruto unique and forbidden jutsu, which would set him on a different path in his ninja journey. Another plot could involve Naruto being adopted by a family outside of the Hidden Leaf Village, and he has to learn to adapt to a completely different ninja culture. He could also bring some of the Leaf Village's values to this new place and cause a stir.
One plot idea could be the Justice League members learning Naruto's ninja techniques. They could incorporate these into their crime - fighting, while the harem aspect adds a layer of relationship drama and support among the characters.