I’m not buying stuff from the market, only in-game or in the Gaijin Store. Would like for it to be under 5000 Golden Eagles if possible. I’m fine with any kind of aircraft. Thank you in advance.
In the words of Top Gun 2,

I need to grind faster cuz my ground br will pass my air br and ill have no cas plen. AND I NEED A CAS PLEN!
As the other guy said, skill matters, but I would recommend early Ki-84. It has really strong flight performance for 5.3. It isn’t going to go faster than the P51 H, but it is still fast and only gets outturned by spitfires and yaks. The guns are relatively low strength with only 2 50s and 2 20s, but planes in this game are fragile enough for them to be workable.
Japan is not the country for cas planes gurl
If he wants Cas, ED should not be playing Japan.
Im gonna grind to top tier and top tier needs cas. plus its a relief from the pain of 7.7 stock germany
KI 84 or J2M both are good
Cool; however, if you are going into Japan with the same mindset as Germany, then you are completely failing to understand that Japan functions more as an aggressive support nation. No one vehicle can do anything you are asking. To the standards depicted. Ki-84 is an excellent aircraft and has 2 250kg bombs; however, going by what you want. Japan cannot provide it. Unless you prefer 2 aircraft in your lineup, one with heavier bombing capabilities and one with primarily fighting capabilities. It was always separate.
its ok ive played basically every nation to a ceratin degree
The J7W1, and J2M5 type 5 with APHE ammo are very good at killing tanks with its guns. If you want to drop bombs and be able to dogfight too, the N1K2’s and Ki-84’s are what you want.
The problem is, he wants “CAS,” and none of what you suggested can provide such. Too likely what he’d want.
Speaking as a Japan main who plays around that BR the most out of any BR, and who spends most of my air time playing CAP/light CAS in GRB, and who has spaded all the tech tree planes, most of which I spaded almost entirely from playing CAS/CAP in GRB lol:
Ironically for CAS specifically the best premium plane Japan has is… The A6M5 Ko. As CAS specifically it is strong right up until 7.0 because GRB forces enemy air down low and plays perfectly to the Zeros strengths. You also get a decent 250kg bomb that is pretty easy to aim and drop, and the Type 99s ground belt API rounds can go through the roofs of Panthers, Shermans etc if you come down vertical on top of them.
Just dont expect to bother playing it in ARB because at 5.7 it is one of the most over BRd aircraft in the game right now and trying to play it in ARB is a waste of time.
If you want something that can be good at grinding in ARB as well, for prems Id suggest the A7M1. It is faster than the Zero, turns almost as well, and still has 20mms and 13.2mms, but much worse bomb load. It also rolls pretty slow, so Id recommend it more if you intend on playing ARB but the A6M5 is better at GRB specifically.
The J2M5 (Type 5) also exists and is an extremely good airframe, but it only has 2x 30mms which can be good at killing ground and air, but Id think it will be less consistent with that armament. IMO in a prem you want consistent performance instead of something gimmicky. I havent flown it but thats just what Im guessing from looking at it.
The FW190 is useless in GRB, they are free meals for anyone with a brain flying CAP. They dont like being down low and take a lot of effort to stay alive in. Likewise the Ki-61 is a pretty bad airframe in general. I would not recommend it.
For tech tree planes, the A6M5/Otsu are good for the same reasons as the Ko. Id just take the base A6M5 and you can slot it into more lineups with its lower BR, for almost identical performance to the Ko. (50 less cannon rounds though). I dont use the Otsu because same BR as the Ko and not prem lol. The A6M5 Hei has heavier armament but is heavy and fat and slow.
A7M2 is the same as the prem A7M1 really. Be weary of the super wide convergence of the guns. They are very far out in the wings which makes your convergence pretty bad and strafing a bit harder.
The Ki-84s will be your next best bet. 2x 250kg bombs and strong flight performance, though the Ho-5 cannons arent as good against ground targets as the Type 99s.
The N1K2s I also quite enjoyed playing in GRB with quad Type 99s, and decent manouverability. Though when I spaded them they still has the 4x 250kg bomb option that gaijin removed for no reason, though the Ki-84 is a stronger airframe. N1K2s should be 5.7 really.
The J2Ms are great at CAP, limited in CAS though. They are strong energy fighters but require some proactive gameplay, watching for and then setting up for enemy planes before they get there so you can engage them from an advantageous position. They have limited bomb options as well, though the same Type 99s.
I know Spookston did a video on the J7W1 and everyone and their mother is flying it now. Yes the guns are good but the airframe is awful. You’ll strafe one or two targets then get shot down. I spaded it before they added the ground belts to the guns lol, in GRB. I hated the thing. It was rough.
None of the twin engine heavy fighters are good at CAS. They are all better at high altitude. Though I did spade them all in GRB lol, flying almost exclusicely CAP.