The following is IGN's walkthrough for December 24 (12/24) in Persona 5.
This guide takes place after the completion of the final Palace, starting from when the Phantom Thieves are standing together in Shibuya.
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Afterschool
Despite the hardships and losses, you won and the people of the city rallied behind you like never before. Perhaps it's time to celebrate as you friends suggest if you're up for it.
Evening
Unfortunately, not all stories have the happiest of endings. Sae will find you wandering around Shibuya. Sae will ask you the hardest thing you will have to do in this game: turn yourself in. It's the only way to ensure that Shido pays for his crimes.
If you don't turn yourself in, your friends will most likely get caught in the crossfire with you. Because of that, you have no other choice.
Before you go off with Sae, you might get an invitation to spend Christmas Eve with someone if you have a romantic relationship. Spend time with one of your requests, but don't let them know what's to come of you. It would break their heart to know.
We spent time with Makoto and were gifted a Wristwatch. This item carries over into a New Game + and boosts reputation gained from spending time with someone while having a Persona from their Arcana in your roster.
Spending time with Ann will have her gift you Earmuffs. This item carries over into a New Game + and boosts reputation gained from spending time with someone while having a Persona from their Arcana in your roster.