I assume that there is no hotel in Japan which offers shower only. Which means there is a bath tub witj shower everywhere. On the other hand, there are many places which you have to share the bath room with other guests. These places include ryokan type inn and hostels.
Shower can be located at the bath tub as same as in Europe or shower can be located next to the bath tub. Usually Japanese wash their bodies outside the bath tub and bathe inside the bath tub. Which means you can put the hot water inside the tube before you wash you body. After washing your body., you can enjoy the bath.
Therefore Japanese tourists also bathe in European hotels even in summer and bath tub is almost must request for Japanese tourists or definitely prefer much more with bath tub than shower only.