One common theme is the power of friendship. Since all three characters value their friends deeply in their original stories, in fanfictions, it often shows how they form new bonds with each other across different universes. For example, they might start off as strangers but end up as great allies.
Sure. One great Naruto, Luffy, and Ichigo fanfiction is 'The Trio's Adventure'. It has an interesting plot where the three characters from different universes team up to fight a common enemy. The story does a great job of mixing their unique abilities and personalities.
The "Negative Fruit" in One Piece was one of the superpowers that Luffy encountered for the first time in the story. The scene where Luffy and his gang fought against the "Negative Fruit" appeared in episode 598,"Luffy and Luffy!" Adventures in Two Worlds.
One common theme is the battle between good and evil within Ichigo. His normal self represents the good, while Dark Ichigo represents the more primal and sometimes malevolent side. Another theme is self - discovery. As Ichigo grapples with Dark Ichigo, he often discovers new aspects of his own power and personality.
Well, I know a fanfiction named 'Twilight of the Ichigo'. In this story, the author vividly depicts the psychological struggle between Ichigo and Dark Ichigo. It also involves some other characters who are affected by this internal conflict. Another fanfiction is 'Eclipse of the Self'. It shows how Ichigo tries to come to terms with his dark side, which is full of twists and turns.
They might have all kinds of adventures. Ichigo could use his Soul Reaper powers in the magical world of Hogwarts. Maybe he'd face off against dark wizards with his zanpakuto. Dark Ichigo, being more chaotic, might get into trouble with the Hogwarts rules and end up in a duel with some of the more hot - headed students.
Maybe Naruto uses his shadow clone jutsu to surround Ichigo and keep him safe from any approaching threats. The clones can act as a first line of defense, alerting Naruto of any danger.
I'm not sure about a specific 'Ichigo and Orihime lemon fanfiction' title off - hand. But you can often find great ones on fanfiction websites. Just search for 'Ichigo Orihime relationship fanfiction' and look through the results. You might have to sift through a bit to find the ones that are well - written and suit your taste.
There could be Byakuya. He would be shocked and disappointed by female Ichigo's betrayal as he might have seen her as a promising comrade. Also, Rukia. Since she and Ichigo have a special bond, her reaction to Ichigo's betrayal would be very emotional. And then there's Aizen. He could be the one who tempted or manipulated female Ichigo into betraying, seeing her as a useful pawn in his grand schemes.