Yeah Kurenai told me that you still have to get your first Rainbow on DMM.
I don't know if this will help you but i am a strong believer of an old theory:
Roll the Normal Gacha until you get a Silverpot or three Bronzepots in a row. Then roll the actual Gacha you are aiming for. That should increase the chance to get a rainbow in the next few rolls.
That was the theory back then when i started playing Nutaku last year.
I don't know if that theory has any substance to it but it worked for me this month. And today i have got three golds after i used that trick.
Could be just me but i think i have more luck this way.
Anyway i hope you will get your first rainbow soon