The fun is happening at the Tsuutenkaku building, so head to the far right and wait out front. Five Union members will show up to stop you. Now you get to fight two more (Tomotaka and Oonishi). If you force them back into a corner just off the screen they won't be able to jump kick you, which means you can deal a great deal of damage while they try to block you. You get a lovely 2243 EXP from this battle. You'll then automatically enter the tower and face yet more opposition.
This is yet another one of those battles where enemy replacements seem unlimited. After an almost unending battle you'll receive a wonderful 14,645 EXP. You can't leave the tower until this part of the story is complete, so if you want to consume any healing items do so now. If you have earned the Sleep Ki power by now use that here as it will completely heal you. Continue to the left. You'll find Kizaki on the ground. He tells you where Masaki is. Continue to the left. A thug will notice you and run off. Follow him up the elevator and he'll attack with three buddies. Defeat them for a decent 1036 EXP. Head to the right and go up and you'll reach the east side of the tower. Head to the right. You'll see two more of Masaki's men fallen in battle, and then you'll be attacked. When they're done with head to the right and up to reach the north side of the tower. Here you'll see Masaki take out four guys and then disappear up some stairs. Follow him. Masaki will ask Ogura why he is trying to take over the city, and then Masaki will take Ogura down. After all that, there is a sound and Masaki falls down. It turns out Yoshihiro shot him, and taunts you to come to Osaka Harbor to get Miho back. Masaki gives you the Dragon God Ring, which deals incredible damage. Now just work your way down the tower and give anyone foolish enough to confront you an up-close look at your new ring.
Back on the ground, use the Bike Key to return to Umeda. Save and heal up. Osaka Harbor is the final stage of the game, so if you want to spend any Prepaid Cash Cards you should do so now. Once you reach level 27 you will earn the Mach Punch, an incredibly powerful close-range attack. If you work your way up to level 27 before visiting the harbor things will be a lot easier. When you are ready, use the Bike Key to reach Osaka Harbor.