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 the fanfiction, Naruto could show his genius in leadership, just like Minato. Minato was respected as a leader. Naruto may inspire others around him with his determination and positive attitude. He could come up with innovative plans to protect the village and its people, much like Minato did. Also, Naruto's ability to understand people's feelings and bring them together could be a sign of his genius in this aspect.
First, Minato would isolate Naruto to prevent the spread of the illness if it was contagious. He'd then research all he could about Naruto's symptoms. He'd make sure Naruto was in a warm and clean environment. Minato would also talk to Naruto, even though he was just a baby, believing that his voice could give Naruto some sense of security. He'd be very gentle when changing Naruto's clothes or cleaning him, always with a loving touch.
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 plot could be that Minato discovers baby Naruto is sick. He might use his ninja skills to search for a rare herb that could cure Naruto. Minato would face many challenges on this quest, like dangerous animals or rival ninja clans. And when he finally gets the herb, he returns to Naruto and nurses him back to health, strengthening their father - son bond.
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.
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.
Well, Minato might constantly be by Naruto's side in the fanfiction. He could prevent Naruto from taking on any dangerous missions, even if Naruto is capable. For example, he may interfere when Naruto tries to join a risky battle against a powerful enemy, saying it's too dangerous for him.