Wanna ride mainstream wave? Buy G-SHOCK watches. Do some research on more sought-after models. Rare JDM ones too.

Japan-branded toys like Takara Tomy, Epoch, Tamiya are considerably cheap there. Even after conver to RM. Cheap as in half-price from TRU and Hamley's here.

Also, Hello Kitty merchandise. Even at the street market also they're selling the original Sanrio's one.

Some shop offers tax-free purchase for tourist provided you show them your passport, so asked them on that. VAT in Japan is 8%, that's quite a lot.