I asked steam support how to start a fresh game of Aragami, this is their reply. Does this seem reasonable?

Hello,

I apologize for the delay.

Currently, there is no official feature that allows the deletion of cloud data for a game. However, you can follow the process below to attempt to manually overwrite this data.

Important: before doing any of the actions below consider backing any files that will be removed to a separate location until you confirm it worked as you desired. Please note that this process is not supported so we will be unable to provide any additional instructions regarding it should you choose to do it.

Make sure the game is installed, it needs to be installed for the files to be found.
Disable cloud functionality for the game (right-click the game in your library -> Properties -> General -> Untick "Keep games saves in Steam Cloud for Aragami")
Navigate to the account's data page for your cloud saves at: https://steamhost.cn/account/remotestorageapp/?appid=280160
On this page, you will see each file currently in the cloud for your account for this game. These files can be located at:
%USERPROFILE%/AppData/LocalLow/159142230/
Navigate to the location for the files on your computer and delete any files you wish to remove from the cloud in that folder and any sub folders.
Now, launch the game and create at least one new save file.
If that was successful, close the game and re-enable the cloud functionality for the game.
When you launch the game again, you will be prompted by a cloud conflict window asking you to pick between two options. You want to keep local files by selecting the "Upload to the Steam Cloud" to overwrite your older files.
Now the data for this game should be reset. Note that in some cases the cloud files may have been overwritten successfully without a cloud conflict window appearing. You can check the account data page again to see what is now stored.

You may also wish to visit the Steam Cloud FAQ for additional information about the Steam Cloud.

Steam Support
Lexie C