I think I have dined at Fuji Japanese Restaurant on every one of my Bangkok trips. Their menu is extensive, reasonably priced and the portions are good. Their insistence of having bamboo interpretations, be it graphic or plastic, is another matter altogether. Ditto for the random pots of ikebana going amok.
With more than 60 branches in Thailand, this feisty Japanese restaurant chain practically dominates the oiishi market of the Thai F&B category. There are probably in every big mall of Bangkok. And I am a rabid fan of their coconut freeze.