Most Fire Mains I have faced have been pretty easy to beat(if they are within my power level).
The only ones that tend to be hard are the Fire Mains with like 6k power more than I do lol.
I play a Breezie~
The easiest way I have found is to focus the Scarlet Blaze as quickly as possible and destroy him...
They tend to be really squishy though they do TONS OF DAMAGE lol :P

There's really no other better option. Just destroy the Scarlet Blaze with your best combo as soon as you can and you don't really have to worry about him.

Having Kurenai is great! You can't really "buy" her anyways...so money is not an obstacle...you just have to work hard and do your arena missions. All Free Players should have her. 500tokens a day and missions stack up...so if you don't do them today...you get another 2 the next day and always @200 per mission. 1week = 1400tokens possible right? Plus you can get extra Fragments doing Elite Instances.

If you have Kurenai in your team and you get hit with a Debuff...you might end up sending it back to one of the enemy team's good ninjas. I have had times where the enemy Neji acupuncture Hinata only for the acupuncture to bounce back onto one of the enemy ninjas trying to use a Mystery Skill(it was funny). Neji wasted his acupuncture and caused another ninja to lose his Mystery Skill. So having Kurenai against the Scarlet Blaze can prove VERY Useful.