A SNEAKY Schwarz is All You Need

IS3 D15, Ending 4 Izu'mik, Source of Ecology
No 6* except Schwarz.
Izu'mik is a boss that summons a myriad of offspring with 46261 HP and 2000 DEF, heavily favoring AoE damage over single-target damage. However, single-target physical damage applied enough times is the same as AoE damage.
BGM
魔导之阵 - Signal-E (Touhou: Lost Branch of Legend OST)
Magia - Kalafina (covered by Nerissa Ravencroft)
Suite Subterranean Animism - Active NEETs
Mars the Bringer of War - Gustav Holst (conducted by Herbert von Karajan)
Antidichlorobenzene x Paradichlorobenzene - Len and Rin Kagamine (arranged by An Alternate Act)
Operation Fake Idol - starpolemic (Idol by YOASOBI, Operation Fake Waves by Skylar Funk)