In USD/JPY at 150.00, one dollar (base) costs 150 yen (quote). Profit and loss on a trade is initially in the quote currency and converted to your account currency.
The quote currency determines the pip value: on pairs quoted in USD, pip values are fixed in dollars; on others they fluctuate with the exchange rate.
Example: a 50-pip gain on 1 standard lot of USD/JPY is 50,000 yen, which at 150 is about $333, not $500.
Related: base-currency, pip, major-pairs, exotic-pairs