What could be the possible reasons for Naruto being cold and calling Tsunade mom in the fanfic?

One reason could be that Tsunade showed him a great deal of care and concern that was similar to a mother's love. For example, she might have healed his wounds or protected him in a way that made him feel like she was family. Another possibility is that Naruto was longing for a motherly presence in his life, and Tsunade's actions towards him filled that void. She could have also given him a sense of stability and security that he associated with a mother - son relationship.

It could be due to a new jutsu he's trying to master that has some side effects on his emotions. Maybe it's a powerful ice - based jutsu that's making him cold in nature as well.

It could be due to a personal loss that has hit him really hard. Maybe he lost someone very close to him, like Jiraiya all over again, but this time it has broken him in a way that he shuts everyone out. He might also be under the influence of a new power that he doesn't fully understand yet, and this power is affecting his emotions, making him cold as a side - effect until he learns to control it.

One possible reason could be a misunderstanding. Maybe Tsunade received some false information about Naruto that made her think he was a threat to the village, so she took actions that ended up hurting him.

It could be related to some sort of external influence, like a curse or a dark chakra that has infected him. This could be slowly changing his personality from the warm - hearted Naruto we know to a cold - hearted version. For example, if there was a powerful enemy who placed a curse on him that targeted his emotions.

One reason could be a mission. Maybe he gets a top - secret mission that requires him to leave the village under Tsunade's leadership without her direct involvement. So he has to leave without much notice.

One possible reason could be that Naruto is so focused on his goal of becoming Hokage. His mind is occupied with training and achieving power, so he seems cold to Sakura. He might not have the time or mental space to show her more warmth.

It could be due to some sort of chakra imbalance caused by the intense events at the Summit.

Maybe he realizes that the shinobi world is too corrupt. There could be political intrigue and power struggles that go against his ideals. He has always fought for peace and unity, but if he sees that the system is beyond repair, he might choose to quit. Also, he could have a family situation that requires him to step away from the shinobi life. For instance, if he has a child with special needs that demands his full attention.

Maybe Naruto discovers some dark secret about Tsunade's past that she has been trying to hide. For example, something related to her lost loved ones. Naruto, in his usual straightforward way, confronts Tsunade about it without realizing how much it would hurt her, and thus makes her cry.