It's not based on a true story. The plot and characters were crafted by the writer for creative purposes rather than being drawn from real-life events.
Well, 'unseen' might imply that it's something that has not received a great deal of attention yet. When it's 'based on true story', it indicates that the core or some elements of it are drawn from real - life occurrences. For example, there could be a small - scale documentary about a local hero that not many people have watched, but it tells a real story from that area.
One way is to research the context of the story. If it's set in a particular time and place, look into historical records of that area. For instance, if it's a story set in a small town during the 1950s, check local newspapers from that time.
One example could be some local historical reenactments that are only shown in small community theaters. They are based on true events in the local history but are not widely known outside the community.
I haven't actually read this specific story. But generally, a story about an unseen patient could involve things like a presence that the medical staff can't physically see but can sense in some way. Maybe there are strange noises or events in the patient's room that seem to be related to an invisible entity.
It could be a rogue Death Eater who has mastered a new form of invisibility spell. This Death Eater might be seeking revenge on those who opposed Voldemort.
The four Grandmasters were the Qing Emperor, who had hidden in the depths of the Palace for more than 20 years, Shou Ye Liuyun, the Northern Qi Imperial Advisor Ku He, and the Guardian God of Dongyi, Sigu Jian. However, there was no mention of the people who had not appeared, so there was no way to know.