1. You will need a white commando I wouldn't waste time battling it out with the Yakuza just find a white commando interrogate him and take him near Takagi's Elevator release him and let him go and he will open it for you

2. Find Takagi in the next area shoot his bodyguards armed with the assault rifles first they can cause alot of trouble and kill Takagi next and unlock the door interrogate the red yakuza he will reveal the next location but its locked there is a secret entrance behind the painting find the key on the coffee table near the dead assault shotgun cop

you can use that if you want but only just shoot a few its a waste of time killing all of them you will never win find the computer in Takagi's Office and it will say 4 minutes before the door unlocks itself

I wouldn't bother holding them off remember the red yakuza soldier I told you about he is in the kitchen area next to the room where you found the key grab him and interrogate him , release him follow him to the computer and he will unlock the door for you then find the painting its to the left of the elevator press cross watch out there is more armoured opponents just use quick kills on them interrogate if you need a health boost go to the corridor and quick kill another guard on the turret gun and behind him is the elevator level complete.