Nagasarete Airantou/WMG

The Reason why Ikuto always passes out when things are getting sexual is that he never got any before he came to the island.

 * His first attempt to leave the island ended with him in a coma, because he had never got farther than an accidental grope and kissing in real life his coma world can't replicate it so it crashes every time it's about to happen. Since he is a teenager though and very horny, it always comes back to sex.

Ikuto will start to use two sword style of fighting

 * About all of his major wins in fighting have come from going from a one handed stance to a two handed stance. Eventually he will just skip the middle man use two swords so he can counter everyone's speed advantage over him.

Suzu is Ikuto's sister

 * Judging by Takatora's resemblance to Ikuto, Michiru's mother's reaction to Misaki, and the fact that all the men were swept away, Ikuto's father must be the now embittered Takatora who adopted Misaki after she stowed away on the boat. Which has some unfortunate implications if you think about how close Suzu and Ikuto have become over the course of the story...
 * If I am reading this correctly then Misaki and Ikuto are not really related which might explain why she seems to want, and sometimes act like Ikuto is her boyfriend.
 * In Chapter 126, Ikuto's grandfather, aboard a boat searching for Airantou, suggested he might disinherit his son, Ikuto's father, if his new wife bears him a new son. Takatora was standing right behind him when he said that. Cut to Ikuto's dad in Japan sneezing. In short, Ikuto is not Takatora's son. Besides, Ikuto was already two years old before the men of Airantou were swept away by the big wave.

Karaage is training Ikuto to be his successor.

 * Not much more needs to be said, but one can assume that Karaage just wants to be a family man now a days with maybe a hint of Stealth Mentor so he is training Ikuto to take his place in the more strenuous parts of being the Western Leader.

Airantō is really The Garden of Eden
The island is a complete paradise with no real troubles or worries. Man and beast can communicate and live in harmony and it's completely isolated from the outside world, except for a chosen few. My theory is that the Sea Dragon God is the flaming sword that God put around Eden after casting man out in Genesis. The rest of the animals were allowed to stay and because of constantly living in Eden they changed to be closer to God's form, more human like as we were created in his image, and that's why they can walk and communicate with each other and humans.

The reason why humanity is back on Eden is we are being given a second chance so the Flaming Sword/Sea Dragon, was ordered to allow some people through and it used storms to gain humans for the test subjects in this new experiment. Remember everyone arrives because of some storm or another driving them there. The people there are chosen for their good and kind hearts.

Why Eden is not still perfect though is that sin still exist in the world so disease and pain are still in the island, but just to a much smaller degree than the outside world. The people are put onto the island to see if purity of spirit can exist there even if purity of body cannot.

The reason all of the men disappeared is that the Flaming Sword/Sea Dragon judged them to be ruining the purity of the island so he had them swept out to sea, and a few years later he brought Ikuto to the island because he is about as innocent and pure of a human as possible. Unfortunately this has backfired a little in that Ikuto is too innocent to participate in sexual escapades to start the next generation of humans. The Flaming Sword/Sea Dragon noticed this and brought in Mei Mei is he thought that Ikuto was not getting it on because of cultural differences not realizing that his own criteria is what is jinixing his attempts at purity.

Makun the genie will play a much, much bigger role in an upcoming story arc.
In one of the earlier chapters (the one involving the spirit with a daughter that looked identical to Ayane), Makun is featured amongst the "very powerful entities" on the island, alongside the Southern and Eastern Lords and several silhouetted figures. What what it be like, then, if the cute little genie really cut loose and started abusing his power...?

Ikuto has a weak Anti-Magic field
This is why he can touch ghosts, and why Chikage's spell in chapter 22 affected him and Suzu the least. This is also the reason that he was able to escape the Dream World and how it affected him differently. It's not perfect Anti-Magic, but it does give him some resistane to super natural phenomenon or at least mess it up a bit.
 * Chikage's magic didn't affect Ikuto and Suzu completely because Suzu's house is so far from Chikage's.
 * That's what Chikage thought, but she wasn't really sure. I'm not saying it's Touma's right hand just enough to mess with large area of effect things not specifically targeted at him.