The students work in groups and try to decide whether to use which or that. One member comes up with their answer. After everyone has brought their answer do an answer check.
As for which one to use I looked it up online and I came up with this rule.
Use 'that' when the information distinguishes the objject from other objects. 'I live in the house that has a green door' means the other houses don't have green doors. Use which when you are providing additional information but not identifying information. 'I live in a house which has a green door' means other houses might also have green doors.
Well, I think that's the way it works.
Honestly this point isn't really worth teaching at this grade level and I try to avoid it unless pressed.
I'd follow this up with a writing activity where the students discribe things visitors might find interesting in Japan. Maybe use a rule where one sentence must use a relative clause.