The idea is to have a mini-Snowverflow effect that lasts for one attack only. But that one attack does Half the boss HP.
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You NEED Iroha LDCA for this to work. I used Shelke LDCA also to fully charge Rosa's EX at the start, otherwise you must wait until she uses EX before bringing Prishe in.
Rosa is there for her Overflow buffs. With her AA, EX and LD buffs up she provides a whopping +75% overflow all by herself
The steps to achieve the one megaton punch is
1. Get Rosa EX, AA and LD buffs up. This is to maximize overflow.
2. Get Garnet BT aura, AA and Iroha LDCA up
3. Bring Prishe in, use AA and BT+. Iroha LD gives her huge BRV refund
4. Keep this until her next turn, do not do any HP attacks on launch.
5. Use Prishe LD. Boss dead
0:00 Setup
2:18 Garnet BT Mode
The reason I popped her BT mode is to quickly bring boss to 50% without increasing the turn count
5:00 Summon
Pop summon immediately after Prishe uses BT+
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