What does G rank do past 20?

[HanChN]

[P.Rampage]

You need to reach rank 21. After 21 it does nothing.

[Exbrune]

The character will receive a milestone (Gachikoi) and receive a certain buffs for their stats. I think it would be G 21 at minimum. Check fandom.

[DarkMatter]

Gachikoi and Fandoms in general work differently now in 0.6. G Rank isn't a requirement anymore at all.

[Peshmerga]

Fandom levels are gained by earning XP. XP are earned thru clearing of stages, 1st time clears give more xp, subsequent clears gives less xp.

G. Rank/gacha dupes also give XP to Fandom levels, but are capped G. Rank 21.

[The Wise Wolf]

Anything past 21 (initial + 20 dupes) is only bragging rights.