One idea could be that Naruto, in this fanfic world, is emotionless due to some dark magic. In the Bleach universe, he could be a rogue soul reaper who doesn't follow the normal rules because of his lack of emotions. For example, he might befriend Ichigo but in a very cold and calculating way, using Ichigo's power for his own ends without really feeling any guilt or friendship in the true sense.
Perhaps Naruto was experimented on by some powerful being in the Bleach - Naruto crossover world. This made him lose his emotions. His new goal could be to regain his emotions by collecting certain spiritual items in the Bleach universe. Along the way, he meets Rukia and they form an unlikely alliance. Since Naruto is emotionless, he approaches battles and challenges in a very different way than the normal Naruto would, which could lead to some unique and exciting plot developments.
In an 'emotionless Naruto fanfiction', it could be that Naruto loses his emotions after a great loss, like the death of Iruka Sensei. He shuts down emotionally and becomes a lone wolf, focusing only on missions. However, his friends, especially Sasuke, realize that he needs to regain his emotions to truly be himself and start a journey to help him.
Well, perhaps a plot where Orochimaru manages to get his hands on Naruto and uses some dark experiments to turn him into an emotionless tool. Naruto then starts to carry out Orochimaru's bidding, like stealing valuable scrolls from other villages. Or maybe in a parallel universe, the Akatsuki capture Naruto and brainwash him into an emotionless tool to use against the Hidden Leaf, and his friends have to find a way to break the spell.
Perhaps Naruto is cursed by a powerful jutsu that turns him into an emotionless killer. He begins to hunt down the shinobi who he believes are threats to the Hidden Leaf, not caring about the consequences. However, his friends like Sasuke and Sakura notice the change and try to break the curse. They embark on a journey to find a way to reverse the effect while also protecting Naruto from himself.
A possible plot is a tournament - style crossover. Characters from both Naruto and Bleach are invited to a special tournament in a neutral dimension. This would lead to some really exciting match - ups like Sasuke vs. Byakuya or Naruto vs. Renji. They would fight not just for victory but also to prove the superiority of their own world's fighting styles. Along the way, they might learn from each other and form unexpected alliances.
One idea could be that Naruto and Ichigo accidentally swap their powers. Naruto has to deal with the Soul Reaper powers in the Bleach world while Ichigo tries to handle chakra in the Naruto world. It would lead to some really funny and interesting situations as they both struggle to adapt to the new powers and the different cultures of each universe.
One idea could be that Naruto wears the emotionless mask to hide his true feelings of pain and isolation after a major event in the village. He might be using it as a way to distance himself from others while he figures out his new place in the world. Another plot could involve the mask being a magical or cursed item that slowly starts to change Naruto's personality, making him more cold - hearted than he really is.
Another plot could be that Naruto was experimented on by Root to be emotionless. He is then pitted against his old friends in a battle. His friends try to reach out to the old Naruto inside him during the fight. This leads to a series of internal struggles within Naruto as he starts to feel the faintest glimmers of his former emotions resurfacing.
One idea could be that the characters from Naruto find themselves in the Bleach universe during a major Hollow attack. Naruto's skills in combat and his ability to sense negative emotions could be really useful in the fight against Hollows. For example, he could use his Shadow Clone Jutsu to confuse the Hollows while the Bleach characters use their Zanpakuto. Another plot could involve a neglected character from Naruto, like Rock Lee, being sent to the Bleach world and training with the Soul Reapers to gain new powers and prove his worth. He could learn Kidou techniques and combine them with his Taijutsu.
One idea could be that Naruto and Ichigo meet in a dimension where their powers are combined. They have to fight a new, powerful enemy that threatens both their worlds. For example, a villain who can manipulate the energy of chakra and reiatsu at the same time.
One idea could be a scenario where Ichigo and Naruto meet in a strange dimension. They initially misunderstand each other but then realize they have a common goal of protecting their respective worlds. They could team up to fight a new threat that somehow has the power to destroy both the Soul Society and the Hidden Leaf Village.