It is really cold in February. You will need a coat, or maybe as has been suggested buy one there. Tokyp will be colder than Osaka. I always look at the world weather map to gauge the temperature maybe a couple of weeks leading up to travelling.
Takayama is beautiful. Old post town streets – amazing to walk thru. The temple walk is divine as are the markets every morning – one either end of town.
Shiragawa – national heritage site. You can get there from Takayama. Awesome original thatched cottages. You can stay in wonderful, very hospitable ryokans
Kurashiki is beautiful with its waterways and old buildings.
Nagasaki, Hiroshima, the island of Miyajima, Okinawa, and the island of Iriomote – absolutely divine.
Get a Jr rail pass and enjoy, enjoy.