THE HOMELESS MEN AND THE CATS Edit
As you leave your hideout in 2-3, a few bums are trying to help a couple of kittens. Meow at them to get them to calm down, then go get them something to eat. You can buy Milk at someplace like the M Store on the north side of town.
The cats will reward you with the Tiger-Striped Cat Pendant and the White Cat Pendant, as well as a note. Go to the Theater Underground B2 and look for the room with the wooden floor, then explore the shining light on the wall above the desk.
The next clue takes you to floor B1, at the base of the escalators from the Kamuro Tunnel. Examine the gleaming red light on the wall to find a third note. Go back to B2 and look for the room with two picture frames high on the wall, then check the bookshelf. Beat up the two homeless guys, and you'll receive the Cat's Key and the Underground Mall B-3 locker key.
You can now name the cats whatever you want. Their new "owner" will take up a position right outside the Theater Underground hideout.
As a follow-up, when you get around to opening locker B-3, it contains 50,000 yen. Give it to the homeless guy for 5,000 XP and the Cat's Key... which you can turn around and pawn at Ebisu for 50,000 yen. The Cat's Key does not appear to have any other actual use.
OLD YAKUZA, NEW TRICKS Edit
Starting in 2-3, there are two yakuza arguing near the Children's Park, north of Theater Square. After speaking with them, talk to Katagiri in Tenkaichi Alley. Take out the punks who're pummeling him.
Go off and amuse yourself somehow for a while, then return to Tenkaichi Alley. In gratitude, you'll receive 2,000 XP and the Trials of the Ancient Fighter King, a book that teaches you how to make Hungry Wolf Gloves.
BROTHER AND SISTER 1 Edit
As you're traveling through the Underground Mall, you'll get your pocket picked by a boy. Pay 1,000 yen to one of the homeless guys at the end of the Mall to learn that Tadashi ran into the underground parking lot.
You'll find Tadashi on the northeastern side of the lot counting your money. Speak to him, and he'll take you to meet Tadokoro the debt collector. Commence the pummeling. After you've significantly reduced Tadokoro's payroll, Tadashi gives you a Chance Stone. You also earn 5,000 XP.
NICE CATCH Edit
If you try to take a taxi, you'll find that the docks are one of your potential destinations. Once there, speak to the fisherman by the water to receive the Fishing Champ magazine. You can also buy bait from him and use it to play the fishing minigame.
The third thing you catch will always be an Attache Case, which will inexplicably be very difficult to pull out of the water. Defeat the yakuza, then return the case to the jewelry store employee near the water. Your rewards are a Ruby and 5,000 XP.
RUNNING WOMAN Edit
Descend to the Theater Underground B3 to find a woman being menaced by a group of yakuza. Take out these five guys, then speak with the woman.
Having done so, there's now an ambush by a few more guys waiting for you at the subway entrance in Theater Square. A third group is in Pink Alley, as the club scout mentions in passing after the last fight.
After defeating those two groups of men, you can catch back up to the mysterious woman in the Millennium Tower Underground. Defeat a final group of Shady Men to receive Saori's gratitude, a Player's Piece, and 5,000 XP.
REASON FOR REVENGE Edit
After you've cleared "The Homeless Men and the Cats," going to the northern part of Theater Avenue results in an encounter with a trio of Kamarocho Men. Take them out, and on your next trip through the same area, Morimoto will bring more men with him for a rematch. Take him and his cronies out, then beat down his boss Iguchi.
As a reward for helping the homeless, you'll receive an Elegant Umbrella, an Iron Nail, a Banker's Piece, and 5,000 XP.
RYOGUJO BOUNCER Edit
Once you've completed "Brother and Sister 1," Tadashi appears in the Theater Underground hideout. Visit him there, and one of Tadokaro's men will arrive with a job offer. Go meet Tadokaro on Park Boulevard, and he'll show you to Ryogujo.
After a short cutscene, you'll receive 300 free chips to gamble with if you like. When you get around to leaving Ryogujo via the elevator, you'll need to deal with a few street punks. They're slightly tougher than the normal variety, but beating them resolves the substory and earns you 5,000 XP.
MOTHER AND CHILD Edit
After completing "Running Woman," go into the Kamuro Tunnel behind the coin lockers to find Takeda. Agree to become Makiko's bodyguard, and when she runs off, go find her at the Shichifuku Parking Lot. Brutalize the trio of stalkers to receive 5,000 XP and a Diamond.
Numai the politician shows up in front of Millennium Tower after you complete "Mother and Child." Offer to be his lookout.
During Numai's speech, talk to the two street punks over on the left by the Millennium Tower sign. Take them out for 5,000 XP.
25 YEARS Edit
You must complete "Brother and Sister 2" for "25 Years" to become available. There also seems to be a strange glitch in effect where "25 Years" will not fire unless you switch characters at some point between finishing "Brother and Sister 2" and going to Shichifuku Street.
That said, go along the south side of Shichifuku Street to meet with Tadokoro's subordinate. You'll find your target, Motoyama, in the homeless tent city near the taxi stand in the Hotel District. Despite being homeless, he's kept up his training, and this can be a slightly challenging fight on the higher difficulties. Return to your hideout in the Theater Underground to receive 3,000 XP.
Tadokoro's subordinate is waiting for you outside the Theater Underground hideout after you complete "Ryugujo Bouncer." Go meet him behind Millennium Tower, then escort their "Client" across town. Don't let any of the hitmen you run into along the way do any damage to the Client.
The trick is that the hitmen are always focused on the Client and will generally try to ignore you. For Saejima, that can be a problem, as he's just slow enough that this can be a complication. Take out three hitmen to complete the substory and earn 5,000 XP.
BROTHER AND SISTER 2 Edit
After you complete "Ryugujo Bouncer," go back to your hideout for a cutscene.
Go back south to Nakamichi Alley and brutalize the punks outside the Orchid Palace Mahjong Parlor. You'll automatically proceed to the roof, where you'll be up against Hayase and about twelve guys, who come into the ring almost as quickly as you can take them out. Your rewards for finishing this job are 5,000 XP and an Eye of the Dragon.
BROTHER AND SISTER 3 Edit
After you clear "25 Years," go back to the Theater Underground hideout to meet Tadokaro there. He wants you to meet him at the Coliseum in Purgatory.
You'll be put up against three weapon-wielding opponents, which basically means you can't block. The first is Chef Chang, who's got a knife; the second is Headhunter Kariya, who's wielding a poleaxe; and the third is Ozawa, who comes in with a pistol. Just as with the last time you fought in the Coliseum, you cannot use items at any time.
After the bout, use the sewers to get back to Children's Park. Beat Tadokaro in a chase sequence, then punch his teeth down his neck. He has more health than you'd expect, but seems to have very low defense, and should drop in seconds. You receive 5,000 XP.
BROTHER AND SISTER 4 Edit
Finally, it's time to rescue Akiko. Go back to your hideout in the Theater Underground and talk with Tadashi. Go chase him to Theater Alley and commence to pummeling, at a rough guess, all the yakuza in Kamurocho. After you overcome three waves of goons, you'll receive 10,000 XP and a Seal of the Dragon.
GREEN SHADOW Edit
Talk to the two angry homeless guys by the escalators in the Kamuro Tunnel, then go downstairs and talk to two more, who are standing in the stairwell by your hideout. Try to enter the hideout and you'll see a new cutscene.
Go to Children's Park and talk to the Doubtful Assistant Director. Buy two Miso Paste Cucumbers at the M Store nearby, then leave one of them on the manhole in Children's Park. Saejima will conclude that he needs richer bait, so go to Sushi Gin on Showa Street and pay 750 yen for some Kappamaki.
Return to Children's Park and place the Kappamaki on the manhole to catch... well, something Kappa-esque. Chase him down to receive 5,000 XP and a Stun Gun.