A B777 FLT CREW RPTED THAT RJTG VECTORED THEM TOWARD AN ACR B777 DURING APCH TO NRT; CAUSING A TCASII RA TO WHICH THEY RESPONDED WITH A TURN AND CLB.

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I WAS THE PNF; THE FO WAS FLYING THE ACFT WITH THE AUTOPLT ENGAGED. IT WAS EARLY AFTERNOON IN VFR WX WITH SOME HAZE. WE WERE LEVEL AT 6000 FT ON A WESTERLY HDG AT 250 KTS; BEING VECTORED BY NARITA APCH FOR AN ILS APCH TO RWY 16L AT NARITA INTL ARPT. THE CTLR STARTED VECTORING OTHER FLTS TO HOLDING FIXES; AS THERE WAS APPARENTLY GOING TO BE A RWY CHANGE TO RWYS 34L&R. I LOOKED DOWN AT MY CHARTS BRIEFLY TO SEE WHERE THE HOLDING FIXES WERE IN CASE WE WERE GIVEN HOLDING INSTRUCTIONS. AS I LOOKED UP; IT SEEMS THAT ALL 4 OF US IN THE COCKPIT SIMULTANEOUSLY SAW A LARGE AIRPLANE ABOUT 4 MI AHEAD OF US HDG S; JUST TO OUR R FRONT. HE WAS TURNING TO EITHER COME DIRECTLY TOWARD US OR GO THE SAME DIRECTION. IT TOOK A FEW SECONDS TO REALIZE THAT HE WAS COMING DIRECTLY TOWARD US AT THE SAME ALT. THE FO DISENGAGED THE AUTOPLT AND BEGAN A R TURN JUST AS THE TCASII 'TFC' ANNUNCIATED; FOLLOWED ALMOST IMMEDIATELY BY THE 'CLB' ANNOUNCEMENT AND THE PRIMARY FLT CTL DISPLAY. AS THE FO STARTED THE CLB; I ANNOUNCED; 'ACR XYZ IS CLBING TO AVOID TFC.' I REALIZED THAT MY XMISSION MAY HAVE BEEN BLOCKED; SO I SAID IT AGAIN IMMEDIATELY; JUST AS WHAT APPEARED TO BE AN ACR B777 PASSED BENEATH MY WINDOW. I XMITTED TO NARITA APCH THAT WE WERE AT 6500 FT; DSNDING TO 6000 FT. WE WERE GIVEN 2 FREQ CHANGES AND VECTORS TO THE FINAL APCH TO RWY 16L AT NRT. I WAS MOST SURPRISED AT HOW QUICKLY THAT SIT DEVELOPED AND PASSED. WE PROBABLY WOULD HAVE DONE THE SAFE MANEUVERING EITHER VISUALLY WITHOUT TCASII OR ON INSTS WITH TCASII; THIS TIME WE HAD BOTH. MAYBE THE OTHER ACFT BEGAN A DSCNT BECAUSE OF HIS TCASII -- I DON'T KNOW. I AM GLAD THAT HE DID NOT DECIDE TO CLB; BECAUSE IT WOULD HAVE BEEN A VERY CLOSE CALL! I BELIEVE THAT AS THE ACR AIRPLANE WAS TURNING; HE WAS FACING THE SUN IN THE HAZY SKY; SO THAT PROBABLY RESTR HIS VISION. SUPPLEMENTAL INFO FROM ACN 629669: APCHING LAKES INTXN AT NARITA; WHILE LEVEL AT 6000 FT; ANOTHER ACFT APPEARED AS A TA THEN AS AN RA DEAD ON THE NOSE AND HIGH ASPECT TO OUR ACFT. I RESPONDED TO THE RA BY CLBING 500 FT WHILE THE CAPT HANDLED ATC COM.