Persona 5 Royal

This achievement ties to the boss of Kamoshida's Palace. To trigger the boss fight, you'll first need to traverse all the way up to the Treasure Room set ahead of the stairs in the throne room, then after completing the cutscene where you need to plant in a calling card to Kamoshida in the real world to make his Treasure visible, you'll get a prompt of whether to leave the Palace now or hold off to find all the Will Seeds and treasure chests and other hidden goodies. Once you're all settled, fast travel to the Castle entrance and leave the premises, then you'll advance to the next day at school, where you'll need to hold a meeting at the hideout to conjure and post the calling card on the school bulletin boards. You'll then advance another day and you'll start back at the Castle entrance. Fast travel to the last safe room that's past the hallway next to the throne room, save your game, and then enter through the opened throne room doors all the way up the stairs to the hallway leading to the Treasure Room. Open said room doors to find Kamoshida's crown, where a series of cutscenes will play that the Phantom Thieves take the crown, before Kamoshida intervenes and eventually transforms into Suguru Asmodeus Kamoshida.

At the start of battle, Kamoshida will utilize a Volleyball Assault attack, who can damage his target one to three times in one go. When your turn comes to battle, attack in any way you wish except for moves that consume SP, as you'll need to save it for later when it comes time for Kamoshida's Gold Medal Spike attack. Keep with this pattern until Kamoshida calls for Libido Boost, a healing spell consisting of eating sets of human legs stocked in the cup of the Trophy of Obsession covering his midsection. There Morgana will recommend destroying the trophy to take away the option for Kamoshida to repeatedly heal himself. Attack the trophy like you've done since the start of battle until you destroy it. Then another cutscene plays out and you'll perform an all-out attack, and this is where Kamoshida will bring out his Gold Medal Spike attack, using one of his students to serve up the volleyball for him to spike, starting with Mishima. Select Guard for all your party members to significantly reduce damage and more importantly boost the odds of survival for your party. After surviving the initial attack, Kamoshida will dismiss Mishima and call Shiho into the fray to set up another Gold Medal Spike. Morgana will ask you whether to attack Kamoshida or Shiho, choose the latter, and now you can unload your strongest moves, as she holds weakness affinities for all attacks. When you start your turn, use your strongest attack for Joker, then pass the baton to Ryuji and use either Lunge, or if you leveled him up high enough, Head Butt. This would leave Shiho around 1/4 of her HP gauge left, which should be enough for Ann and/or Morgana to finish her off. As a reward, Kamoshida will have no more 'slaves' as set ups for his volleyball attacks, and so he'll only have his Golden Knife attack at his disposal. While it can do a good chunk of damage, you can get around it with Dia healing spells for any party member whose health is at the lowest in the group. Upon being rid of Shiho, Morgana will ask whether to go for the crown on Kamoshida's head or attack head-on. Choose the former, as you'll send a party member out of battle to go and knock the crown off Kamoshida from above, which will leave him demoralized and will be suspect to greater damage from attacks in this state and make beating this boss easier and faster. Once you get in an attack on your next turn, you'll get a prompt whether it's time to send a party member out of battle to go for the crown. Press to select Yes, then pick Ryuji, as he does not hold any healing spells in his moveset, while Joker, Ann, and Morgana do, you want as many windows to heal as open as possible. For the crown knockoff to succeed, you'll want to attack as much as possible to keep Kamoshida from spotting the party member gunning for his Treasure. You'll need about four to five turns before Ryuji successfully ascends to the upper floor. From there Kamoshida will notice someone in your party has disappeared, and by this point Ryuji will go knocking the crown off his melon. Kamoshida will then be dejected, making him easy pickings. Unload your strongest attacks until he is beaten.

The kicker here with this achievement (and with all other Palace-related achievements in the game) is that it doesn't unlock immediately after beating Kamoshida. Rather, it unlocks when you advance to May 2nd (5/2) and you play through the cutscene when the real Kamoshida barges into the Shujin Academy gymnasium and confesses his crimes, all the while rescinding the expulsion requests for Joker and Ryuji. After Kamoshida finishes speaking and follow-up dialogue from the students concludes, your achievement will pop on screen.