So the new guy appears and he has drifted to the island much like Yamada. He regains consciousness and they have a little talk, probably about what he remembers. Chika then show up shortly afterwards and joins in on the conversation. For some reason Yamada walks off and when he returns back he sees the two embracing each other, misunderstanding the situation. He now thinks hes the boyfriend Chika mentioned but in truth she has no boyfriend as said in one of the translated chapters (I believe ch. 3). Don't ask what they were really doing because I don't remember.
Ok... from this point on I can't remember the events that happen next exactly and I can't find raws to help since mangahelpers took them down but nothing major happens so I'll skip to the end.
Being overwhelmed by the pressure now he suddenly run off deep into the island not carring what happens to him. He gets to a cliff and without thinking tries to jump to the other side. Unfortune for him he does not make it (looks like he hit the other end of the cliff pretty hard)and falls to the bottom where a river or lake resides. Once Yamada hits the bottom, he loses consciousness and doesn't awake until sometime later with Chika by his side (probably saved his ass). Batter and beatin it appears Chika did some banaging work on him and they start to talk for a while, I'm pretty sure its about whats going on with Yamada. More talking is done and I think did they eventually make up. Everyone is happy and in the lake area they are in Yamada decides to jump into the water and get something to eat. Now... this is where the weird shit I talked about earlier starts to happen.
Once in the water, Yamada dives in and out a couple of times and soon begins to lose consciousness again. I think its probably due to blood lost or being stress out but who knows and he blacks out. When he wakes up again apperantly now hes in a life boat being rescued from the sinking ship
(think about the story Yamada and Chika talk about in ch. 3 about the boat incident). Confused he starts to look around and figure out what going on. It turns out there are several other life boats with students and the ship incident seems to have happened just minutes before. Yamada now looks frantic and looks for Chika but sees no sign of her. The last shot of chapter 6 shows the ship and its people abandoning it.
Strange huh... My guess is somehow Yamada went back in time or something and now has to relive those moments but I need translations to confirm. Thats all I can gather and remember from the raws I saw and no I don't believe there is more than 6 chapters out since the series is relatively new and those raws came out maybe about 2 weeks ago. Hope this answers some questions.
One last thing I want to mention, the relationship between Chika and the new guy doesn't seem anything special, in fact for some reason she seems upset at him for something. As for what that is I don't know...