Yakuza 6: The Song of Life

This achievement is a serious grind. Before we begin, I strongly recommend completing the Kiryu Clan story in Kamurocho (complete Onomichi first) That way you have both Chief Advisor (x2 exp) and Chief of HQ (x1.5 exp) positions opened up to give a couple characters exp boosts.

Next, I'll go over the codes:

Super Rare:
ATPERCENTDRAGON - Kazuma Kiryu 100
Rainmakerokada0 - Kazuchika Okada (100)
kiryusavemepleaz - Daigo Dojima - (90)
0INTHEREDAKIYAMA - Shun Akiyama - (90)

Rare:
TheSecretJoAmon - Jo Amon (90)
NoRestForKazumaK - Kazuma Kiryu (80)
RainmakerMrOkada - Kazuchika Okada (80)
MYSTRYMANSATSUKI - Satsuki (80)
TheSupernovaRana - Kushida (70)
the6thheadofTojo - Daigo Dojima (70)
ELingobernable00 - Tetsuya Naito (70)
MisterTokyoDome0 - Hiroshi Tanahashi (70)
detectivemanDate - Makoto Date (70)
shibatagotosleep - Katsuyori Shibata (70)
AdreamingAkiyama - Shun Akiyama (70)
NagataLockNagata - Yuji Nagata (70)
TheSupernovaRana - KUSHIDA (70)
BLACKPANTSKOUMEI - Komei (70)
HeaintNoJoeShmoe - Joe (70)
BestCoachSodachi - Sodachi (70)
0Banshee0Muzzle0 - Evil (60)
BinwanProducer00 - Toru Yano (60)
0HERCULESCUTTER0 - Manabu Nakanishi (60)
MasterofDropkick - Ryusuke Taguchi (60)
00IshiiDriller00 - Tomohiro Ishii (60)
FirebirdSplasher - BUSHI (60)
AMasterbartender - Bartender (60)
PURORESUNEWJAPAN - Captain New Japan (50)
STRONGMACHINEDDT - Super Strong Machine (50)
ITSTHEGEDOCLUTCH - Gedo (50)
shouldertoleanon - Masao (50)
OHNOONOMICHIOKUN Ono Michio (50)

Common:
7R30M9ZDUH0MJIA1 - Jo Amon (60)
T2OMQ7FM5KBJPOUR - Goro Majima (50)
S66X7BAQN4ECAEE9 - Kazuma Kiryu (50)
VRJR9A7SX9Z6MMTV - Taiga Saejima (50)
PNJTEF9STVONK4U9 - Satsuki (50)
M5BXOKQRSIELV19D - Daigo Dojima (40)
UVHVD2H7WI95GHNL - Makoto Date (40)
3QXI6YIGSH03DETX - Ono Michio (30)

Now, for the strike team I'm using:
Kazuma Kiryu (SR)
Kazuchika Okada (SR)
Diago Dojima (SR) - Needs to be the first deployed (can be the 3rd if you're deployment is maxed out)
Shun Akiyama (SR)
Amon (R)
Hiroshi Tanahashi (R) - He's extremely valuable because of Warrior of Love, which revives downed party members at full health. You do need to redeploy them, however.

My total strength at the time of this post is 67178.

Now, to get the most bang for your buck, you should play The **** Army Part 2 (or 3 if you're feeling confident enough).

Kazuchika Okada (my Chief Adviser) averages 17,000-20,000 exp when I run Part 2 and he's currently level 60. Kiryu (my captain) is level 50.

You can increase your strength by putting soldiers under yourstrike team members and soldiers under those soldiers. You can further increase your strength by leveling up your soldiers using exp you get from the main game.

Finally, try to keep Hiroshi Tanahashi back. You need him alive in case you lose one of your men.

NOTE 1: You can view your progress in the cell phone menu. Just pause and scroll to Clan Creator. However, it's the number of times you've played, not the number of times you've won. If you know you're going to lose a battle, you can quit with and the counter won't go up. I know because I've tested it myself.

NOTE 2: If you don't have Warrior of Love available, you can wait it out. Once you have enough deployment points, you can bring back whom you need that was downed.