A lot of things related to Mashu:
- Mashu gets upgraded to a 5*, having a complete revamp of her kit by turning her into a mix of support and DPS. Her new class is Shielder Paladin which is functionally the same as Shielder.
- Mashu can now be grailed to 120 and you can reach Bond 10 with her, unlocking a Bond CE that increases her Attack by 30% and gives her a 30% HP Guts.
- You can get Mashu coins by completing missions that will unlock upon completing the chapter, so you can grail her to 120 and unlock more append skills. The missions are related to a new node in the Camelot and in the LB6 map, you have to use Mashu there and you have to defeat the enemies there. You also have to do enough damage with Mashu, but honestly this is a non-issue because she hits really hard there. The mission is repeatable in case you don't reach enough damage.
You unlock both the Shielder Class Score and the Ruler Class Score after completing the chapter. Rank in the map is increased to A and you get access to the free missions in the OC4 map.
As for item rewards, you get a blue key for the Class Score, one grail and you get the usual CE to commemorate clearing the chapter