Unlike other floors, it's as easy as campaign. By the way, Refithea, Veronia, Granhildr combo can clear all floors.

☆☆☆ Underground 21F ☆☆☆

Utilizing Iris' charm, so if you are using Serendia, make sure Serendia won't buff Iris.

1. ★6 Ceres+10
2. ★6 Isabel+15
3. ★6 Serendia+15
4. ★6 Ayan+14 (Kill 3, 2, 5, 12|9|11)
5. ★6 Iris+15 (Charm 4, 8, 9)

☆☆☆ Underground 22F ☆☆☆

1. ★6 Ceres+10
2. ★6 Serendia+15
3. ★6 Michaela+15
4. ★6 Rene+15 (Kill 6, 7)
5. ★6 Joseph+9 (Kill 8, 2, 3, 4, 9)
6. ★6 Britain+10 (Kill 5)
7. ★6 Mora+9 (Kill 1)
8. ★6 Acha+10 (Kill 10, 11)
9. ★6 Jayden+15 (Tanking)

☆☆☆ Underground 23F ☆☆☆

1. ★6 Ceres+10
2. ★6 Naressa+10
3. ★6 Isabel+15
4. ★6 Sarubia+15
5. ★6 Joseph+9 (Kill 7, 11, 2, 4)
6. ★6 Iris+15 (Charm 9, 12, 5|Kill 8, 10, 3)

☆☆☆ Underground 24F ☆☆☆

Using Iris' charm, and Acha+Sloan's counter.

1. ★6 Ceres+10
2. ★6 Naressa+10
3. ★6 Iris+15 (Charm 3)
4. ★6 Isabel+15
5. ★6 Joseph+9 (Kill 5, 6, 7, 8)
6. ★6 Acha+10 (Kill 2, 4, 9, 10)
7. ★6 Sloan+10 (Kill 2, 4, 9)

☆☆☆ Underground 25F ☆☆☆

11 will copy taunt from Iris, that will prevent Mora to attack the boss. So 11 needs to die quickly by counter.

1. ★6 Iris+15 (Charm 9, 2, 3)
2. ★6 Serendia+15
3. ★6 Mary+10
4. ★6 Ceres+10
5. ★6 Michaela+15
6. ★6 Joseph+9 (Kill 5, 12, 10, 9, 7, 8, 3)
7. ★6 Horan+10 (Kill 6, 11)
8. ★6 Sarubia+10
9. ★6 Mora+9 (Kill 1)