1. Buy 2 memory resonance/month 2. Try to have 1-2 weapon resonance when new S debut, this included farm weapon reso shard in norman. 3. Priority to sss a free characters such as Ayla, Selena, Alisa 4. Priority to sss leap characters who is still in the meta such as Vera, Empyrea, Karen. At this point you will have selection shard left a lot and you will find out who to use with, Rosetta is best choice for me because her shard available in the shop and battle pass mission for so long, when she sss+ I can convert her shard to exchange any S shard in the shop, the cost is 3:1.
For Amplifier, It's not satisfying if not SSS. i personally will skip 21, Coz i save BC for directly SSS arisa and Lamia. And I still have SSS+ Liv empyrea project.