This is just building off of what KabukiArcade said.
At the casino for about 15,000 or so chips you can buy treats, specifics, miracle gels, special gels, limit bottles, barriers, and one other item. On your first play through you are limited to 15 each, but if you sell 15 of all 6 of these items at Yamanju, it nets you about 187,000 gald.
So in short this is incredibly easy to get even on your first play-through, as this whole process takes maybe 5-10 minutes a trip.
Actually there is a slightly faster way, though this one is more luck based. If in addition to the items listed above you buy also buy 15 holy avengers, it costs about 500,000 chips, but it also sells for about 500,000 gald. So basically you can continue to play poker and hope to get long double up streaks. It takes a little luck but its not that hard to get over 500,000 chips on one hand; and I have at least 3 times gotten over 1 million at which point you can no longer double up.
Some additional tips for winning chips or things I have noticed:
- Jack and 10 are tricky cards, common sense would dictate you would go low on these cards, but honestly I have actually lost because I should have gone high almost as many times as I won by going low
- 2 and Joker are the only guaranteed wins due to the fact that if you draw the same card whether you say high or low you win; I have quite often got burned because I went low on Ace and a Joker appeared, and on 3s and 4s I have gotten burned with 2s
- occasionally you should be content with smaller wins in the 3000k -10000k, dont always go for the big streak, banking some of these smaller streaks will allow you to slowly build your count and also allow you to afford more loses, because 500 chip loses can add up
- for the long streaks, 100K or more you will probably have to make tough calls once or twice, ie cards in the 7-J range will appear; on some of my longer streaks I called high on Jack, or low on 7 or 6; this is honestly luck
- be wary of something like getting K, K , Q --> common sense dictates low, but these streaks almost seems like traps and if you go past 3 or 4 face cards they throw an ace in there; same thing with streaks of 2, 3, 4, 4 I have been burned quite a few times for calling high
- this is just an observation but its seems the higher your starting bet the trickier high low is; almost every time I got a four of kind (never got anything higher) a queen would be thrown out followed by a high card or the reverse
- this is not quite like real poker, if you have two 2s and an ace, discard the ace, and go for three of a kind of two pair, versus trying to get two aces or more
- if I tend to have one or two face cards, I hold those, and usually I at least broke even; ie if i draw an ace and jack and numbers, I hold the ace and jack
- I do not know what the theoretical limit is for most chips in one hand, my best hand was 1.5 million at which point I hit the limit of turns; so theoretically if you hit 4 of a kind of higher on your first hand and manage to win out on high low you could top 1.5 million but I don't think by too much
The last key tip, check the value of your inventory, I did this 80 hours into the game so my inventory was worth over 2 million; so you dont actually have to get 10 million, build your gald to 8 million, save sell your stuff and then after the achievement pops restart