Quiet Pearl

Quiet Pearls are a specific currency used to obtain Awakening Soul Shards of SSR units.
Both recurring Quiet Pearls purchase and exchange for Soul Shards are available during specific events though recurrence itself is not very predictable.
=How to Obtain=
Glittering Pearls are expected to be a recurrent reward in various seasonal events 
However the most common way to obtain it is via the recurring Pearl Purchase event by spending Diamonds:
Pearls	Cost	Max Purchases	1	150	250
=Exchange=
The exchange rate is always 1:1 with Soul Stones.
Assuming one starts with a 1* awakening unit, here is the number of pearls required:
To 	To	To	To	To	To 	To 	To
From	 	1*	2*	3*	4* 	5* 	6*
From	1*	- 	20	70	170	320	520
From	2*	- 	- 	50	150	300	500
From	3*	- 	- 	- 	100	250	450
From	4*	- 	- 	- 	- 	150	350
From	5*	- 	- 	- 	- 	- 	200
==Awakenings==
All SSR units having an awakening are available for Soul Shards exchange.