In order to make Kiryu the best Fighter around, you will want to look to increase his stats as you progress through the Main Story. You can easily find and increase Kiryu's stats by clicking on the Options Button on your Phone, followed by selecting the Skills Tabs. By doing so, Kiryu will be able to a variety of things better, including surviving longer in fighters, being able to withstand more hits, and even causing more damage to his opponents when he himself lands an attack. In order to increase his stats, you will need to use the EXP you earn throughout the game.
Need help earning EXP? Then definitely check out our Guide on How To Earn EXP in Yazuka 6!
When looking to increase Kiryu's stats, it is definitely recommended to focus on his Core Stats when first beginning the game. You can't go wrong with using your hard earned EXP towards increasing his Overall Health, Attack and Defense. On top of this, it would also be wise to further boost his Evasion, as it will help you dodge the attacks your opponents try to deal. Furthermore, if you have some extra Purple and Green Category EXP, definitely consider using it to further increase Kiryu's Heat Gauge, allowing you to earn Heat Orbs quicker during a fight.