Well, perhaps in this fanfiction, Ichigo in Mugetsu form is stuck in a dimension where time and space work differently. He could start losing control of his Mugetsu powers and has to learn to master them again in this new environment. Along the way, he meets a character who has knowledge about his situation and helps him on his journey, which involves facing various challenges and foes.
One possible ally could be a powerful mage from a different anime in the crossover. This mage could help Ichigo understand the strange magic or energy in the new world he is stuck in. Also, Uryu might be an ally. His Quincy abilities could complement Ichigo's powers in Mugetsu form as they face new threats together.
You can start by exploring his inner turmoil more deeply. Mugetsu Ichigo has a lot of power but also a great burden. Show how he copes with this in the new crossover setting. For example, if he's in a world with different power systems, how does he adapt his existing powers?
One idea could be that Mugetsu Ichigo finds himself in an alternate universe where he has to team up with his other - self from that universe to defeat a powerful new enemy. Maybe this enemy has the ability to nullify his Zanpakuto powers, forcing him to rely on new and creative combat strategies.
A powerful rogue Shinigami who has turned against Soul Society and is seeking to use Mugetsu Ichigo's power for his own evil purposes. This antagonist could have some dark secrets related to Ichigo's past or his family, which would add more depth to the story.
A plot could involve Mugetsu Ichigo losing his memories after a battle and ending up in the Fairy Tail world. He starts to learn about Fairy Tail magic and even develops some new skills by combining his existing powers with the magic there. Meanwhile, Fairy Tail wizards are trying to figure out who he is. When a powerful enemy emerges that is related to the Soul Reaper world, Ichigo's latent memories start to return, and he and the Fairy Tail gang must work together to defeat it.
It could be Aizen from Bleach. Imagine if he somehow found a way to cross over into the Fairy Tail world. His devious and powerful nature would make him a formidable antagonist. He could manipulate the dark guilds in the Fairy Tail world to do his bidding and try to gain control over the powerful magic there, all while being a threat to Mugetsu Ichigo who he has his own history with in the Bleach universe.
Well, 'ichigo in fairy tale mugetsu fanfiction' might be about Ichigo in a fairy - tale - like setting within a Mugetsu - related fanfiction. It could involve Ichigo having adventures in a magical world that is influenced by the Mugetsu concept. Maybe he'll encounter strange creatures or gain new powers.
Maybe in the fanfic, Mugetsu Ichigo teams up with some unexpected characters from another series. For example, he could meet characters who have unique abilities that complement his own, and together they face a powerful common enemy that neither could defeat alone. This would lead to some interesting character interactions and power combinations.
One interesting story could be about Ichigo exploring new powers in his Permanent Mugetsu form. Maybe he goes on a journey to a hidden dimension where he has to face unique challenges that only his enhanced form can handle.