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This is more a question and a minor nitpick, but:
When did Sona get the reverse ability/spell in the actual series?
The first time I recall seeing it is after the peace talks during the Sona/Rias rating game before the Loki arc, and Azazel thought she got it from fallen angels in vol 11 (Latest volume at this time).
I don't think it is stated, but by Vol. 11 everyone in her Peerage had already mastered it, so I think there must have been some time learning it first.
HigH scHooL DxD
Volume 11
ISBN 978-1-9753-2807-8
Page:128
Azazel(Thinking to himself): BUT... THE SITRI PEERAGE'S "REVERSE" MOVE-THAT'S SOMETHING WE FALLEN ANGELS WERE WORKING ON. DID ARMAROS OR SAHARIEL OFFER IT UP IN EXCHANGE FOR BATTLE DATA?
The Sitri peerage would have had weeks to practice with reverse before they had a the match with Rias's peerage, but the anime and novel are farther along so the source may be known?
That only says they worked with it...
Maybe she got it from wherever the Angels got it from?