@nazrulstylo in the end it's pretty much hinted they are sent to the future based on the mothers prayer.
The pilot thing I don't think is ever really explained but possibly assume he miraculously landed and it's also from the prayer.
Kou chan and hades don't seem to be apart of the ending group so if hes still alive all this time might of kept himself hidden. It is annoying the author never reveals who hades is but I guess just served as just a religious metaphor.
Also the time jump isn't clear it's about 50 years since the island was created and by the time they got on there it's completely run down.
About the bio hazard I pretty sure it's only deadly only if its ingested so I think what they did might of been enough. What I don't get is why some were initially poisoned and what's with the various mummified bodies.
I think a bigger mystery is how Mina knew all these animals weaknesses when they weren't in the sketch book. And if Mina was faking memory loss why.
And it's pretty obvious Akira ended up with his childhood friend.
The only thing that's especially dumb about the ending is the mother created it in hope her son could have fun adventures on it on an island of deadly animals.
Overall it was an enjoyable read.