Glad I wasn't the only one confused. And disappointed with the endings.
Actually, as it was said, he was an investigator who turned into a private detective in order to find his lover who was deported back to his original country. And, this is just an assumption, after searching for 7yrs and not finding anything, the lover contacted Maki's 'friend' who in turn contacted Maki, that he'll be waiting on the island, or something along those lines.
The disheveled look is simply because of how he priorities looking for Hotaro than his appearance, plus he's broken hearted for 7yrs, a guy would certainly look like shit if that happens. xD
and if you ask why Hotaro contacted Maki's 'friend' instead of Maki, it's because he didn't have any contact information of Maki, while Maki's friend gave him a bussiness card...
These stories began good but the endings were meh. I didn’t even get the last one at all. So the detective never left the island I’m assuming cuz he was all disheveled and wandering? And the guy showed up but then called the detective stupid? Like he was supposed to know where the guy went?