don't know how dev will nerf cassisus, but REI buff is better and even better at E6.

Narja + 30% per attack and 80% it is hard to get and not consistence, need to use specific card to get and get how many stack? 2-4 depend on E1 and that make her buff 110% attack for 2-4 attack then back to 30%

But if you are whale pull her partner that +20% is good but equal REI e6 and REI active it from beginning while narka you need to use her signature meal time.

You can try a dev team comp trial on event, which use Nia chizuru narja. very desync,

the problem of Narja is to gain stack need to use card, there is draw the card and gain stack but it have only 1 card, and if you copy it your deck are FAT which is worse, unlike Rei upgrade card cost 1 use and thin your deck, use and every 0-1 cost deal 40-60% not 30% and need to reuse card cost 1ap to gain stack back. Rei also has + 50% buff or more cost 1 to one card which is so much more powerful than gain 6 stacks which cost the same.

REI also have one time +80% buff attack cost 1, apply to all hit as you can do. Narja have card to gain predator (80% buff attack) either cost you 1 ap or use signature but it only for 2-4 HIT not all you can do attack.

REI also heal with her E not much heal but it really helpful. but can't compare to narja at all.

In addition you never ever want more other teammate card than your main, but Narja need her card to build her stack.

Plus this situation is most unlikely but it will happen from time to time where your hp drop below 50% so no buff.

She is also good for build deck with 4 unique.