Perhaps the fanfiction starts with Namjoon feeling unwell during a busy schedule. He tries to hide it at first but then collapses. The other members are worried sick. They call the doctor and while waiting, they start reminiscing about all the good times they've had with Namjoon. The cute comic could illustrate these memories in a series of panels. As Namjoon recovers, he's more grateful than ever for his brothers in BTS and they all have a newfound appreciation for each other's health and well - being.
In the fanfiction, Namjoon getting sick might lead to some deep and heartwarming moments. For example, he could have a dream where he's in a magical place and the other members are there as his guardians. When he wakes up, he realizes how much he depends on them and how strong their bond is. The cute comic aspect could show the members in chibi - like forms, with big heads and small bodies, taking care of Namjoon. They could be drawn with rosy cheeks and big smiles as they try to make Namjoon feel better.
One possible scenario in this fanfiction could be that the other BTS members take care of Namjoon. They might bring him warm soup, his favorite books to read while he's sick in bed. Jin could be in the kitchen cooking up a storm to make sure Namjoon gets his strength back. Jimin and Taehyung might be by his side, telling him funny stories to cheer him up. Jungkook could be running errands like getting medicine. And Suga and Hoseok would be there to keep the mood light and positive around Namjoon.