In cultivation fanatics novels, there were usually the following levels:
1. Spiritual disciple: The foundation of cultivation can only use spiritual power to carry out simple operations.
[2. Cleric: A spiritual disciple evolved to be able to use spiritual power to perform more complicated operations.]
3. Spiritual Apprentice: A Spiritual Master who has advanced can operate spiritual power independently and be more familiar with the use of spiritual power.
4. Spiritual Apprentice: Spiritual Apprentice can perform more complicated spiritual power operations and use spiritual power more freely after advancing.
[5. Spirit Lich: Spirit Lich can perform more advanced spiritual power operations and can use spiritual power to create various magical items.]
6. Spiritual Apprentice, Apprentice, Apprentice: Spiritual Apprentice, Apprentice, Apprentice has advanced and already possesses the basic strength of an immortal cultivator, able to carry out high-level cultivation and combat.
[7. Spiritual Apprentice, Apprentice, Apprentice: Has become a true immortal cultivator. Able to carry out various high-level cultivation and battles. Able to control spiritual power and the power of nature.]
[8. Spirit Disciple Disciple
Well, there is some 'naruto luffy brother fanfiction'. Some of them explore how their different powers would interact if they were brothers. For example, Naruto's ninjutsu and Luffy's Devil Fruit abilities could make for some really exciting adventures together. Also, the different worlds they come from, the Hidden Leaf Village and the Grand Line, could be combined in creative ways in these fanfictions.
I'm not sure specifically who the main characters are without reading the fanfic. But they're likely to be characters who are seen as different or 'freaks' in some way, and are involved in a romantic relationship.