POTENTIAL CONFLICT OCCURS WHEN A B777 FLC STARTS A DSCNT THROUGH ALT OCCUPIED BY A COMPANY B747 WHEN RESPONDING TO A SIMILAR SOUNDING CALL SIGN FROM APCH CTLR AT NARITA; FO.

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WE WERE GIVEN A HOLD AS PUBLISHED AT AIRES INTXN 1000 FT ABOVE OUR COMPANY. HIS CALL SIGN WAS ACR Y HHB; OUR CALL SIGN WAS ACR X HAB. THE CTLR SOUNDED NEW AND UNSURE OF HERSELF. HER ANNUNCIATION WAS ALSO A FACTOR. WE BELIEVED SHE GAVE US A TURN AND DSCNT FOR VECTORS TO FINAL APCH. WE READ BACK THE CLRNC AND INITIATED THE TURN AND DSCNT. WE NOTICED OUR COMPANY TFC STILL BELOW US AT 11000 FT STILL IN THE HOLD. WE WERE DSNDING OUT OF 12000 FT AND THE ASSIGNED HDG WOULD HAVE PUT US CLOSER TO THE TFC. WE STOPPED OUR DSCNT AT 11500 FT AND STOPPED OUR TURN. WE MADE 2 CALLS TO TOKYO APCH TO VERIFY OUR CLRNC. THE CTLR THEN GAVE ACR Y HHB (THE TFC BELOW US) THE SAME CLRNC WE BELIEVE TO BE FOR US. SUBSEQUENTLY; THE CTLR GAVE US A HDG AND ALT TO AVOID ANY FURTHER CONFLICT. WE ARE NOT SURE IF THIS INCIDENT WAS A READBACK/HEARBACK PROB OR CTLR ERROR. FOREIGN ACCENTS AND FATIGUE (FLC) (14 HR FLT) ARE BOTH CONTRIBUTING FACTORS IN THIS INCIDENT. TCASII GAVE US AN ADDITIONAL TOOL IN MAINTAINING SITUATIONAL AWARENESS EVEN WITHOUT A TA/RA.