Have him head up either set of stairs into the sarcophagus chamber with the fifty-three sarcophagi plus the broken one, that Ico was placed into. There are half a dozen wimpy spirit demons flying around something or someone on a circle inset in the floor up above in the rear center of the chamber. Have him head up there and start swinging away at them. As each spirit demon is dispatched, it returns to a sarcophagus, which then lights up. He has to rid the chamber of all fifty-three of them before he can get to the nasty queen. You can look about the room during the battle to get a feel for how many are left. They will jump away form Ico the second he turns toward them and will continue jumping away as he persues them. However he can catch them after several of their jumps and particularly if he backs them into a wall. One hit is all it takes to send the essence of one back where it belongs. Some of them will take to flying in circles and may or may not be slayable from the floor. If not jump and swing the sword at those to do them in. Once the melee is over, stairs rise behind the circle in the floor granting access to the four Idol Doors above. Head up there to find that it's Yorda but Ico can get no response from her. Continue up and go open the doors with the sword and head on through into the Throne Room.