Hello minseok,
I'm really sorry about the lost progress, I know how frustrating that is after so many hours. I'm just a fellow user here, so I can't see your account or the game's data, but here's the main thing to know.
A Microsoft account is only used to sign you in to the game. Your character and progress are almost certainly stored by the game's developer or by Steam, not by Microsoft. Microsoft doesn't hold or manage third-party game saves, so we can't restore or look into them from this forum. I can't see which game this is, so I can't be sure how it stores its saves.
Since you could log in after the password change, your Microsoft account probably still exists. It looks more like the game is loading a new or empty profile. A few quick checks:
- Sign in at https://account.microsoft.com with the same email you always used and your new password. If that works, the account itself is fine.
- In the game, sign out completely and sign back in with that same email, not another Microsoft account. A different account would show up as a brand-new player.
If Microsoft says the account doesn't exist or won't accept your sign-in name, these official pages cover that:
- Sign-in helper: https://support.microsoft.com/en-us/accounts-billing/manage/microsoft-account-sign-in-helper
- Username stopped working: https://support.microsoft.com/en-us/accounts-billing/manage/my-username-and-password-have-stopped-working
- Account recovery form guide: https://support.microsoft.com/en-us/accounts-billing/manage/help-with-the-microsoft-account-recovery-form
If your Microsoft account signs in fine but the character is still gone, the next step is the game's developer or Steam support for that game. They're the ones who hold the save data. Share your Steam playtime and achievements with them as proof that the account is yours.
I'm sorry I can't promise more than that, but I hope they can get your character back.