With my strategy, skill wise Joseph+9 is required. Level wise Grosa, and Claris are max level without awakening. For some stages, Grosa needs to take a hit and survive. Therefore equipping viatal x 2 is also required. This also helps to get higher score. Others are at level 1 and skill level is not important.

☆☆☆ Underground 6F ☆☆☆

1. ★4 Deka (Kill 2, 3, 1)
2. ★4 Joseph+9 (Kill 7, 9, 8, 5, 4, 9)
3. ★4 Grosa (Vital x 2 to help higher score)
4. ★4 Denarisa

☆☆☆ Underground 7F ☆☆☆

1. Front attacker (Kill 6)
2. ★4 Joseph+9 (Kill 7, 9, 8, 5, 4, 9)
3. Front attacker (Kill 2)
4. ★4 Grosa (Kill 1)
5. ★4 Denarisa

☆☆☆ Underground 8F ☆☆☆

1. ★4 Corette (Kill 1, 2, 6)
2. ★4 Iris (Kill 4, 3, 5)
3. Front attacker (Kill 7)
4. ★4 Grosa (Vital x 2 to help higher score)
5. ★4 Denarisa
6. Meat shield

☆☆☆ Underground 9F ☆☆☆

Grosa needs to withstand attack from 4. One way to do it is by having barrier from max level Claris.

1. ★3 Edan
2. ★3 Claris
3. ★3 Cordelia (Kill 3, 2)
4. ★4 Britain (Kill 5, 6, 7)
5. ★4 Lian (Kill 9, 10, 8)
6. Front attacker (Kill 4)
7. ★4 Grosa (Kill 1)
8. ★4 Denarisa

☆☆☆ Underground 10F ☆☆☆

Grosa needs to withstand attack from 10.

1. ★3 Edan
2. ★3 Claris
3. ★4 Elijah
4. ★3 Wiggle (Kill 2, 5, 4, 3)
5. ★4 Joseph (Kill 1, 6, 7, 9, 8, 10)
6. Front attacker (Kill 10)
7. ★4 Grosa
8. ★4 Denarisa
9. Meat shield