He uses his skills as a ninja to protect Naruto. He sets up special seals around Naruto's crib to keep out any potential threats. Also, Minato might try to use his chakra to boost Naruto's weak body. He would transfer his own life force a little bit at a time to help Naruto fight the sickness, which is a huge sign of his love.
Minato shows his love through his actions. He goes on dangerous missions to find rare herbs or special medical ninjas who could cure Naruto. He also shares his memories and stories with Naruto, even though he's just a baby. He hopes that these stories will give Naruto the strength to fight the illness, and this shows how deeply he cares about his son.
Minato might show his protectiveness by always being near Naruto in spirit. For example, he could leave behind some kind of jutsu or power that activates when Naruto is in great danger, like a hidden seal that releases a powerful defense.
In fanfiction, Minato's possessiveness might show in his reactions to Naruto's achievements. He could take too much pride in Naruto's success as if it's only his to be proud of. For instance, when Naruto accomplishes something great, Minato might act as if he's the sole reason for Naruto's success and not give enough credit to Naruto's own hard work and the influence of his friends.
One possible storyline could be Minato's struggle to find a cure for Naruto's sickness. He might search through all the hidden jutsu in Konoha, asking for help from the elders and the medical ninjas. Another could be Minato's emotional journey as he takes care of his sick baby. He'd be filled with worry, but also determination to see Naruto healthy. For example, he could sacrifice his own sleep to stay by Naruto's side, constantly monitoring his condition.
In some fanfictions, Minato saves Naruto physically. For example, he might use his teleportation jutsu to appear right in the middle of a fight and whisk Naruto away from danger. In others, he could save Naruto spiritually. He might enter Naruto's mind, like in the fanfic 'Minato's Mind - Saving Mission', and give him the strength and confidence to overcome his inner demons. Sometimes, Minato saves Naruto from a political situation. For instance, in 'Minato and the Hidden Leaf's Politics', he uses his influence and wisdom to protect Naruto from being used as a political pawn.
Well, in some fanfictions, Minato might use his powerful jutsu to break through the barriers between the living and the dead and directly reach Naruto. He could also try to influence the people around Naruto to bring him closer to where Minato is, like using his spirit to communicate with Naruto's friends and convince them to help.
Minato's presence can have a huge impact. He can act as a mentor, teaching Naruto things he never knew about his family and heritage. His wisdom and skills can inspire Naruto to reach new heights in his training and ninja development.
Naruto's character development includes learning about sacrifice and the importance of bonds. In the fanfic, his refusal of Minato could be a sign that he has outgrown the need for a father figure in the traditional sense. He has formed deep bonds with others like Iruka, Kakashi, and his friends. These relationships have made him strong enough to face Minato and say no if he feels it's necessary for his own growth and the protection of those he cares about.
Rin could also be an important character. She could be the one who takes care of baby Naruto's day - to - day needs, like feeding and cleaning. She could also have a special bond with Naruto, perhaps seeing him as a symbol of hope for the future of the village.
He could feel it through a shared chakra link. Since they are related and Minato sealed the Nine - Tails in Naruto, there might be a latent connection that gets activated in the fanfiction, allowing him to sense Naruto's pain on a physical and emotional level.
Naruto could incorporate Minato's sword - fighting skills if he has any in the fanfiction. Minato was known to be proficient with weapons. Also, Naruto might use Minato's strategy of quickly assessing the enemy's weaknesses and then striking precisely at those points. He could even use some of Minato's signature jutsu in a more efficient way, like the Rasengan, but with Minato's finesse.