LoL PBE data suggests upcoming Jhin skin is exclusive to event capsules

If you’re looking to add the upcoming Dark Cosmic Erasure Jhin skin to your collection, you may need to dish out a hefty amount of money to get a chance to obtain it—and only for a limited time.

According to the description of the Cosmic 2023 capsule, which is set to be released with the new Cosmic skins and event alongside Patch 13.17, players will have the chance to earn random skin shards and additional rewards upon opening this item, much like all previous events. However, the description also indicates that players have a chance to obtain Dark Cosmic Erasure Jhin from the capsule, suggesting there is no other way to obtain the skin.