Health insurance as an exchange student?

Hi, so I am going to japan for a student exchange (for 5 months with the possibility of prolonging it for 10 months) and wanted to ask about health insurance. My school doesn't handle it so I have to do it myself and I'm not sure whether for a stay of this lenght I need to register with any japanese authorities or if I should just get a travel insurance from a commercial company? For record, I am from EU so my usual health insurance here is covered by the state until I finish school

In case I need to register in japan, how should I go about it?

Thanks