When Ryuichi starts to run away, a couple of new thugs will appear on the upper level. Watch how they come down to the lower level. That's where you can climb up. If I remember correctly there was a bit of a barrier, but it goes away when the goons arrive. You can hang around and shoot the gangsters, or you can just ignore them. They won't have time to kill you if you keep running. After you climb up, it's pretty simple. Just go up the steps.