Credit to CyricZ for his guides.

This guide is pretty late considering this game has been out for a little over a year on PC, but I thought I would make it as the only other achievement guide available on Steam is incomplete. Hope this helps anyone.

The game itself really isn't difficult to unlock all the achievements for, it's just very time consuming. Only do this if you have the time for it and don't mind wasting it.

You'll have to complete the game a minimum of 3 times. Once on Normal, once on Hard, and once on Legend.

The Plot Thickens
Clear Part 1 of the story.


Cannot be missed.


Reunited
Clear Part 2 of the story.


Cannot be missed.


A Detective's End
Clear Part 3 of the story.


Cannot be missed.


Only One Thing Left to Do...
Clear Part 4 of the story.


Cannot be missed.


Thank You!
Clear the Finale.


Cannot be missed.

Indomitable
Clear Normal Mode without reverting to Easy Mode.


Unfortunately this won't unlock if you complete the game on a harder difficulty, so you'll have to play on Normal either way. I suggest your first playthrough being on Normal, then making a clear game data on Hard so that you have all your skills unlocked.

Heir to the Legend
Clear Legend Mode.


This difficulty unlocks after you complete the game on Hard (even on NG+), so let this be the last achievement you go for after you complete everything else.

Way of the Key Master
Open five coin lockers.


There are 100 coin lockers in the game, 50 above ground and 50 underground. You only need to open 5 for the achievement, however feel free to go for all if you like.
Refer to these guides for the locations of the keys: Above ground[gamefaqs.gamespot.com]
Underground[gamefaqs.gamespot.com]

Substory Novice
Complete or finish four substories.



Substory Helper
Complete or finish twenty substories.



Substory Lover
Complete or finish forty substories.



Substory Champion
Complete or finish all substories.


There are 63 substories in this game, 16 for each character except Saejima, only having 15.
Refer to this guide for all the substories and how to complete them: Substories[gamefaqs.gamespot.com]

Emblem Collector
Collect ten emblems from survivors during gang encounters.


Gang Encounters are a "side activity" exclusive to Kiryu. Go to Theater Square and you'll see a guy named Akaishi, who is part of a neighborhood watch group called Kamurocho Guard, being beat up by some gang members. Kiryu will intervene and beat up these gang members. Akaishi will then thank you, and ask you for your help against these gangs in town. Now, these gang members spawn randomly around town, and you'll notice them because they wear the color of their gang. Beat a certain number of a gang, and you'll be able to face their leader.
After you defeat a gang leader, you'll be done with that certain gang, but you will see some "survivors" of said gang wandering around town. Defeat them and they'll give you an emblem. Earn 10 emblems for the achievement.
Refer to this guide for information on all the gangs in the game: Gang Encounters[gamefaqs.gamespot.com]

Weapon Master
Create one or more weapons for each weapon category.


There are 10 weapon categories. Bats/Clubs, Polearms, Blades, Hammers, Knuckles, Tonfa, Nunchaku, Kali Sticks/Double Swords, Guns, and Others. You only need to create 1 of each category to unlock this achievement.
Refer to this guide for information on modding weapons: Weapon Modding[gamefaqs.gamespot.com]

Revelation Seeker
Acquire three Revelations.


There are 12 Revelations in this game, you only need 3 to unlock this achievement.
Refer to this guide for information on all the Revelations: Revelations[gamefaqs.gamespot.com]

Walking Bank
Possess 10,000,000 yen or more.


There are several ways to easily earn 10,000,000 yen in this game. You can gamble using cheat items to win chips, then exchange those chips for Platinum Plates and sell them. You can complete the game (Normal = 2,000,000 yen, Hard = 3,000,000 yen, Legend = 5,000,000 yen). Tanimura also has a substory (A Dangerous Game) which rewards you with 3,000,000 yen for completing. These are probably the easiest methods to quickly obtain large sums of money.

Akiyama the Hoarder
Earn 1,000,000 yen playing as Akiyama.


Self explanatory. What I suggest is using cheat items with Tanimura to acquire 10,000 casino points for the "Tanimura the Gambler" achievement, exchanging the points for Platinum Plates, but don't sell them yet. Switch to Akiyama then sell them with him. This way you get both achievements easily.

Saejima the Slinger
Purchase five guns playing as Saejima.


Cheapest gun is the 9mm Automatic Pistol sold at the Rooftop Weapon Shop which costs 120,000 yen. Buy 5 of it.

Tanimura the Gambler
Acquire 10,000 casino points playing as Tanimura.


Self explanatory. Just use cheat items and you'll get 10,000 points relatively quickly.
Refer to this guide for information on cheat items: Gambling Cheat Items[gamefaqs.gamespot.com]

Memo Master
Collect all Memos in the Pause Menu.


Self explanatory. Refer to this guide for a full list of the Memos: Memos[gamefaqs.gamespot.com]

Fashionista
Gather at least one outfit from each category in "Hostess Maker."


Note: If you miss this achievement, you can't complete it unless you start a new game.
This achievement requires you to buy one of every type of outfit for the Hostess Maker minigame. There are 23 outfits you can buy, however you only unlock a few every 3 or 4 shifts you complete so this achievement is a bit time consuming. Be very careful not to accidentally complete the minigame too quickly or you won't be able to unlock the achievement unless you start a new game. Because you only unlock a few outfits every 3-4 shifts, it will take some shifts of you not doing anything in order not to reach #1 too early.
Refer to this guide for information on the minigame: Hostess Maker[gamefaqs.gamespot.com]

Star of the Coliseum
Acquire the title "Star of the Coliseum."


While both Kiryu and Saejima can fight in the Coliseum, this achievement is only unlockable by Saejima due to the fact that only he can earn the title of "Star of the Coliseum".
Refer to this guide for information on the Coliseum: Coliseum[gamefaqs.gamespot.com]

Ultimate Challenger
Clear all Ultimate Skill missions.


Ultimate Matches are "challenges" unlocked after beating the game. They are accessible from the Main Menu. There are 10 Melee Matches, 5 One-on-One Matches, 10 Challenge Matches, 5 Team Matches, and 5 Ultimate Matches. Most of them are straightforward, but some can be very annoying.
Refer to this guide for information on Ultimate Matches: Ultimate Match[gamefaqs.gamespot.com]

Fearsome Foursome
Max out all characters to level 20.


You should have this unlocked after beating the game and finishing all substories, however if you don't have it, you can use the Coliseum for Kiryu and Saejima, the IF7-R gives 2,000 exp the first time you beat an opponent, and you can finish a hostess storyline for 10,000 exp.

Gourmet of Kamurocho
Order something at least once at each restaurant.


Here is a list of the restaurants:
Sushi Gin, Showa St
Cuez Bar, Underground Mall
Cafe Alps, Nakamichi St
Watami, Nakamichi St
Pronto, Nakamichi St (Different sets of menu during Day and Night)
Smile Burger, Nakamichi St
Matsuya, Tenkaichi St or Taihei Blvd
Gelateria Kamurocho, Tenkaichi St
Bantam, Millennium Tower St. East
Kyushu No. 1 Star, Pink Alley
Shellac, Champion District
Earth Angel, Champion District
Kanrai, Shichifuku East
Underground Gourmet, Sewers near Eco-Store

Some restaurants e.g Smile Burger give you the option to "take out", you must choose "Eat in" for this to count.

Also, to decrease your health in order to be able to eat, use Squid Bait (available at the Docks) which slightly decreases your health when eaten.

The Joy of Gifting
Have a hostess wear a present you give her.


When you go to a cabaret club and talk to a hostess, you'll have the option of giving her a gift. If she likes the gift, she'll wear it the next time you visit. Here's a list of the hostesses and their preferred gifts (you can purchase them from Milestone in the Underground Mall):
Rio: Strapless Dress
Noa Mizutani: Strapless Dress
Erena Aihara: Strapless Dress
Himeka Kawasaki: Mini Skirt Dress
Chihiro Ikki: Mini Skirt Dress
Nanami: Mini Skirt Dress
Shizuka Saito: Strapless Dress
Maya Mori: Mini Skirt Dress
Hiyori: Strapless Dress
Kyoko: Strapless Dress

After-Work Hookup
Have a hostess invite you on an after-work date.


To go on a date with a hostess, you have to reach 8 hearts with her. Once you reach 8 hearts, you'll receive a phone call from the hostess. The achievement should then unlock.
Refer to these guides for information on all the hostesses and how to raise their heart meters:
Rio - Shine[gamefaqs.gamespot.com]
Himeka Kawasaki - Shine[gamefaqs.gamespot.com]
Shizuka Saito - Shine[gamefaqs.gamespot.com]
Noa Mizutani - Jewel[gamefaqs.gamespot.com]
Erena Aihara - Jewel[gamefaqs.gamespot.com]
Chihiro Ikki - Jewel[gamefaqs.gamespot.com]
Maya Mori - Jewel[gamefaqs.gamespot.com]
Nanami - Elise[gamefaqs.gamespot.com]
Hiyori - Elise[gamefaqs.gamespot.com]
Kyoko - Elise[gamefaqs.gamespot.com]

Business Card Hunter
Receive business cards from all hostesses, including ones you train in "Hostess Maker."


Self explanatory. Each hostess has 2 business cards, one you get from your first visit and one you get from your final visit, you only need the first ones.

Master in Training
Have one of your apprentices win the Rookie Tournament in "Fighter Maker."


Note: This achievement is glitched for some people
This side activity is for Saejima where he trains students at Sodachi's Dojo. To unlock this achievement, one of your students must win the Rookie Tournament. Refer to this guide for information on the Fighter Maker activity: Fighter Maker[gamefaqs.gamespot.com]

Table Tennis Pro
Smash the ball three times in one match.


A smash is basically a heat action. In order to do it, when the ball is going towards your opponent, hold L2. It'll stare at their chest, slow down the action, and build up Heat. When your Heat bar is full, press Triangle when the ball's coming to you to perform a smash. You'll know you did it when a cutscene plays. Refer to this guide for information on Table Tennis: Table Tennis[gamefaqs.gamespot.com]

The Human Jukebox
Sing all songs at karaoke.


Self explanatory. Here are all the songs (do them all with Kiryu):
Otomeiro My Life
Machine Gun Kiss
Pure Love in Kamurocho
Raindrops
GET to the Top!
I Wanna Change Myself
Kamurocho Lullaby
Summer Memories
Where Has Your Touch Gone?
Saturday Night Lover
Shooting Star

Hat Trick
Achieve a hat trick in darts.


A hat trick is three bullseyes in a row. Refer to this guide for information on Darts: Darts[gamefaqs.gamespot.com]

First Carom
Win the first point in Four-Ball billiards.


Self explanatory. Refer to this guide for information on Pool: Pool[gamefaqs.gamespot.com]

Boiled Turkey
Achieve a turkey in bowling.


A turkey is three strikes in a row. You can follow this video to get it easily.

Novice Gambler
Play all non-casino gambling games.


Self explanatory. The games are cee-lo, cho-han, koi-koi, and oicho-kabu, and they can be found in the gambling hall in the Dragon Palace.

Casino Rookie
Play all casino gambling games.


Note: This achievement is glitched for some people
Self explanatory. The games are blackjack, poker, roulette, and baccarat, and they can be found in the casino in the Dragon Palace, or Park Blvd., or Purgatory.

Welcome to SEGA
Play all minigames at Club SEGA.


Self explanatory. The games are UFO Catcher, Boxcelios 2, and Boxcelios, and they can be found in Club SEGA in Theatre Square, or on Nakamichi Street. In order to find Boxcelios, Akiyama has to play Boxcelios 2 three times and befriend the Theatre Square Club SEGA manager and he'll agree to install Boxcelios into the arcade.

Shogi Promotion
Achieve a promotion in shogi.


Self explanatory. Refer to this guide for information on Shogi: Shogi[gamefaqs.gamespot.com]

Seven Pairs
Win a round by forming a concealed hand containing seven unique pairs in mahjong.


Self explanatory. Refer to this guide for information on Mahjong: Mahjong[gamefaqs.gamespot.com]

Captain Two-fer
Successfully hit two panels at once at the batting center.


Self explanatory. Just hit the border of two panels like in this video.

Mr. Outdoors
Golf and fish five times each.


Self explanatory. For golf, you don't have to complete a game so you can just start then immediately quit. For fishing, just cast your fishing rod, you don't have to catch anything.

Kamurocho Iron Man
Traverse 100 kilometers or more.


Self explanatory. Don't use the taxi and you'll unlock it without even trying.

Kamurocho Stampede King
Knock over 100 people you pass by.


To do this, go to Theatre Square and just start running into people. You can only knock people down from behind them, not in front of them. I believe you also cannot do this to women, only male NPCs.

Kiryu the Crusher
Destroy 100 weapons you pick up playing as Kiryu.


Self explanatory. If you use weapons a lot, you'll get it before you complete the story. There's an easy way to do it quickly, go to the east end of Theatre Square. There's a box that has bottles which you can infinitely pick up and break in one hit.

Kamurocho Tree Hugger
Pick up twenty pieces of trash around the city.


Self explanatory. Scattered throughout Kamurocho on the ground are pieces of trash that light up green. Pick up 20 for the achievement.

VIP Member
Become a VIP member at the massage parlor.


Go to Love in Heart on Senryo Ave., and pay for a massage 5 times. That's it.

Master of Kamurocho
Acquire all achievements in the game.