In Japan you can bang your sister if you're both adults. You can't marry anyone closer than first cousins.
I just discovered that
you can marry half-siblings in Sweden. This would mean that he could marry all but one of them there... (He did only have an in-house onee-chan and no imouto, right?)
In which country brother and sister get married?
Sibling marriage is legally prohibited in most countries worldwide. One notable exception is Sweden, where marriages between half-siblings are legally permitted. However, historically, sibling marriage was practiced in ancient Egypt and Inca tribes.