Who is Captain Yoniata from A Town Like Alice and what is their importance?

Captain Yoniata is the young Japanese officer who captures the English refugees at Kuala Panong. He speaks a bit of broken English and lectures the prisoners regarding obeying orders, showing respect, and doing "good things." On the second morning, Yoniata also interrogates the families by groups, dispatching the men to prison camps right away, while the "womans and childs" remain.