I actually found out about this game through Saffron and Aconite's HCGs on danbooru haha

So About the RC it seems this was the reason.
Pretty much close to one of theories I had. This being a sort of promo of some sort.
In this case a "Come back promo".

Silly Nutaku, I never even left to begin with!

Thanks for the free Helenium (Easter) though!

Well in my case it was true.

I left three months ago and only occasionaly visit my Nutaku Account.

Not because i immensely disliked the Nutaku Version (like i did back in February 2017) but just because i have better luck on DMM. More freebies there was also a big factor. I couldn't afford to whale on both versions so i quit.

For the Rainbow i went with Hollyhock. Don't have her on DMM so i got her here.

Now, my Nutaku account beat my DMM account in another area: Rainbow Medals. The other thing dat my Nutaku account has over DMM, more rainbows. DMM does give out a lotta freebies but I never seen Rainbow Medals. Dat was weird but I take it. I do like to play both versions and embrace both their pros and cons

->Open Spoiler<-

I will save 'em for Aizoon if I don't get her w/ my attempt on Voting Gacha - trying to get 50 FK by May 15

For Reissue

Calla's maps remind me of the old maps - so much retries



I beat every reissue, got lucky on Moon Vine, Geranium and I forget the others, so much pain and misery LOL RNG Nodes

As I never quit FKG I’m guessing in practice the Rainbow medals were awarded to anyone who spent more than $35 on the game regardless of their active or inactive status.

The "active" part might be "active payer"

Anyone who in the past spent the prerequisite amount of money, but then spend no more.
At least that makes sense all thing considered.