Who's that Pok- Anime Opening?
Yes you already saw the roses, but I added the background...
And it added like 4Kb of data so Medibang can't handle it! Thank goodness for optimization algorithms.

But guesses so far:
Ouran school
Fate/Stay Night
Rose of Versailes (Ok no one guessed that)
RWBY
Tokyo Mew Mew

What's your guess?

Tip: Trying to read the text in the gif is pointless.