Percy often uses Observation Haki to anticipate the attacks of his enemies. He can sense their movements and intentions, which gives him an edge in combat, especially against fast - moving or sneaky foes like some of the monsters in the Percy Jackson world.
Dumbledore could be the one to teach Harry about Haki. Dumbledore, with his vast knowledge of magic and the unknown, might have come across Haki in his travels. He could recognize the signs of Haki in Harry and take it upon himself to guide Harry in understanding and controlling this new power. He would use his calm and wise approach, just like when he teaches Harry about other aspects of magic.
I recommend One Piece: The Great God Usopp to you. This book is a story about Usopp. It tells the story of how he obtained the League of Legends system through an accidental transmigration and became invincible. If you want to read a One Piece Doujinshi novel with a deceptive cloth as the main character, this book is perfect for you. I hope you will like my recommendation.
In this fanfiction, Naruto's development with Haki could be quite interesting. Firstly, Haki could enhance his sensory abilities even more than his regular chakra - based perception. This would allow him to detect threats from afar and better protect his village. His physical attacks could also become more powerful. He might start to train with different characters who are more familiar with Haki, like if there are any characters from other universes introduced. This could lead to him learning new values and cultures, expanding his world view, which in turn would shape his character in a more complex and mature way.
Yes, in many Naruto fanfictions, authors often give Naruto the power of Haki. It's a creative way to blend the concepts from One Piece (where Haki exists) with the Naruto universe. This can lead to really interesting storylines, like Naruto using Haki to sense enemies' intentions better during battles or using it to enhance his existing jutsu.
Friendship turned to more is a very common theme. Since they start as crewmates with a normal friendship in the original, fanfictions often explore how that can develop into a romantic or deeper emotional bond.
Naruto's use of haki would be a game - changer for his combat skills. Haki has different forms. For example, the Observation Haki could allow Naruto to see the future movements of his opponents to some extent. This would combine really well with his already amazing combat skills like his Rasengan and Shadow Clone jutsu. He could use his clones more effectively to surround and attack his enemies while using haki to predict their counter - attacks.