This page contains unmarked spoilers for the entire manga.
About the merged Amapola/Hainuwele in the final chapter
In the chapter What Can I Do For You Now?
, when Shiina and Jyun see the dragon whose Otohime is a dolphin, Jyun warns Shiina not to touch it because "minds can transfer". Incidental as the line might be, it hints at a very possible explanation for the merged Amapola/Hainuwele seen in the last manga chapter...
After Bungo's death in chapter 65, Satomi must have either committed suicide (most likely by jumping into the sea along with Bungo's body) or otherwise given herself to Amapola; during the process of her becoming an Otohime, Bungo's mind may have transferred as well, leading to Amapola taking a lot of physical traits from Hainuwele. (I don't think it's likely that Bungo himself became an Otohime as well; he'd most likely need his own dragon for that, and Hainuwele was completely destroyed in the final battle.)
The Earth moved to cleanse itself through its choice of dragon-hosts
Never had the chance to read the unexpurgated version, so forgive if this is too obvious. But Shiina seemed to be the least screwed-up of the hosts. Virtually every other child was so intensely alienated, a bad end and worse reaction to that end was assured.
Hoshimaru is Zee-tee
and the series is a very loose adaptaion of the game he stars in
Star shaped orange thing: check.
Cheery on the outside: check
Screwed up and disturbing on the inside: DEAR GOD, DOUBLE CHECK.
Shiina's daughter was not fathered by Takeo.
He was already sterile from the effects of radiation poisoning by the time the two had sex. Shiina became pregnant around that time or after the Earth was "reset" via human parthenogenesis
. There are already so many supernatural events linked to her, so why not that? Her soul is bound to the Earth after all, and Earth goddesses from several myths do tend to have children with no need of a partner. Plus, there's the fact that the daughter looks just like her (could be just a very strong family resemblance, but would also happen in the case of parthenogenesis).