Aetos had been experimenting on two of us at the time. Me, and a Meridian named Dokja. I was implanted a crest that channeled Harmonized abilities, but for Dokja they were implanting a secondary shard. Aetos had lamented that my "compatriots were still present" so that he couldn't pluck a shard from the timestream to do the same to me. It got me suspicious, because he could have always asked the person who turned me in to fetch the shard I had been gifted by Yima.

[Sakura's shard would have held plenty of power. She's a bit of a monster after all. The only "excuse" Rin can think of is that perhaps gifted shards are too weak in regard to their pull to Kenos itself rather than their own inherent power. Yet still, she's harbored her suspicions since.]