Bí Bảo
Growth gear after the second job change, raised with dailies.

Bí Bảo is an Era-only slot. The character receives Bí Bảo Sơ Khai after the second job change, then raises it over time. You cannot buy Bí Bảo rank with cash. The sources are daily activities and dungeon materials.
How to raise it
Do the dailies at Rue and Yanai. Farm materials in Lavalon, Green Forest, Mutisa, Bone Dragon, and similar dungeons. The upgrade NPC is in Odellia, and the window shows the Bí Bảo checkpoints.
In-game events, fan codes, or livestream codes sometimes give a checkpoint or materials. That is an exception, not the main path.
New and old players sit at different checkpoints because of time online. Staff adjust the requirements at some stages so later players do not have to farm the same number of weeks as the first players.
Enhancing Bí Bảo
Bí Bảo uses Tinh Tú Pháp Bảo, +5% success from +5 to +24. See the Enhancement article.
The date calculator for gem checkpoints is on the blog, on the Bí Bảo calculator page. This wiki will attach that tool in a later version. For now, open the calculator on the blog.
The blog lists reference gem rates inside that calculator: Ngọc Phước Báu +240 per day, Ngọc Công Đức +450 per day, Ngọc Thánh Đức +70 per day. Use those numbers as an estimate, and check in game because dailies and events change by season.