Yakuza: Like a Dragon

This achievement is heavily based on your personality stats along with these being Ch 15 Substories. There are several romace options Saeko, Sumire at Romance Workshop Ririka at Hello Work, Iroha at Survive bar, Eri of your party and Ichiban Confections and Miyakoshi at Ounabara Vocational School. I did it with Saeko and Sumire

For Sumire, First get the Romance Workshop to max level which will cost you 20 million Yen, I suggest grinding either the Sotenbori Battle Arena or the better option of the Milllenium Tower Dungeon, getting to Fake Saejima (5mil) and running it back from there. Choose the "Talk with Sumire" option. Eventually you'll have to bring her Bonsai. You can find this and any other flowers at the "Flowers 2 Go" in Hamakita Park. I would suggest buying more than 16 here as you'll need them later. You will also need to max out one stat for each romance, Sumire is Passion. I, personally had to grind for too long to get my passion to Lv 10. Once you get through all the dialogue from each encounter with her (basically telling you how many Bonsai to give her), you'll have a straightforward fight against some loan sharks (all around Lv 17). Once you finish the fight, you'll have 1 of 2 required relationships done along with substory 14 "Something Worth Protecting"

For Saeko it's much more simple. Max out your bond with her (A separate achievement) and have your style stat maxed. Then in survive interact with her, watch the interaction and boom you're done. This should be 2 of 2 (given you went with these 2) finishing off the achievement and substory 47 "Girl of my dreams"

For Eri, you will have to reach rank 1 in the business mini-game along with your kindness level maxed. Interact with her at Survive Bar and you will have the relationship done with her. This will also finish substory 48 "Share Vision"

For Miyakoshi, there is 3 steps to this one. First complete all 21 vocational exams at the Vocational School. The will help your personality stats in a solid way. Link to the answers: https://www.gamesradar.com/yakuza-like-a-dragon-exam-answers...
Second would be to have your intellect maxed out. You will also need to go to the Flowers 2 Go cart in Hamakita park. Purchase 16 bouquets of lilies. You can also grow lilies in the park or at Survive Bar but buying is quicker yet more expensive. Third, talk to Miyakoshi at the school, give her all the lilies, once that's done you should have the relationship done along with substory 49 "Certified Lover". She will also unlocked for Ichiban Confections.

For Iroha, it is a bit easier and is also 3 steps. First, you'll need to have 16 chats with your party (You should already have 16 by now as they're more naturally occurring, these are the ones in the streets and such). Next, you'll need 16 bouquets of roses from the Flowers 2 Go cart. You'll need your Charisma maxed this time. Give Iroha the roses for the relationship and this will also finish substory 50 "Pillow Chat". Iroha will also be made available for Ichiban Confections.

Last is Ririka. For Ririka, you'll need maxed out Confidence and to have Kasuga have tried every job on at least once. you don't have to play the job, but at least change to it (you will also get the "Life Experiences" achievement for having Kasuga in 8 different jobs other than his starting job). Next, you'll need 16 bouquets of pansies from Flowers 2 Go. Go back to Hello Work, do the interactions with Ririka and the relationship will be done, this will also finish substory 51 "The Real me".