Honestly, I think a lot of people go into 'Japan Sinks' expecting a straightforward disaster movie cast. It's more of an ensemble piece where the roles shift as things fall apart. The central figure is probably Koichiro, the geologist whose theories nobody believes at first; he's the Cassandra of the whole mess. His assistant, Ayumi, sticks with him and becomes kind of the emotional anchor.
Then you've got the political side with Prime Minister Yamane, who has to make the impossible calls, and his more pragmatic aide, Riko. Their dynamic shows the brutal calculus of saving a nation. The young guy, Go, and his sister Mari represent the everyday citizens just trying to survive and find their family. Mari's arc, especially when she gets involved with the Self-Defense Forces, really shows how ordinary people get forced into extraordinary situations.
What's interesting is that no one feels like a traditional 'hero.' They're all just reacting, making terrible choices under worse pressure. The roles blur – the scientist becomes a refugee, the politician becomes a figurehead, the sibling becomes a soldier. That fluidity is the point, I think. The ground is literally giving way, so all their fixed roles in society do too.