So, a situation may arise where you are required to install Windows where the only media you have is a USB drive. Now if you're already running Windows, you can do this with the media creation tool.
You can download a Windows 10 image direct from M$ here.

Obviously, we're running Linux ;) So download the ISO image and let's get cracking ;)

USB Prepare

You will need a drive >4Gb (I used a 2Gb :\)

Insert your USB and execute (where 'X' is the drive eg /dev/sda):

fdisk /dev/sdX

I'm assuming there are no partitions defined. So we'll start from scratch.

# fdisk /dev/sdj

Welcome to fdisk (util-linux 2.30.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p
Disk /dev/sdj: 1.9 GiB, 2058354688 bytes, 4020224 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x0003dd8d
-------------------------------------------------------------------------------
Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 
First sector (2048-4020223, default 2048): 
Last sector, +sectors or +size{K,M,G,T,P} (2048-4020223, default 4020223): 

Created a new partition 1 of type 'Linux' and of size 1.9 GiB.
-------------------------------------------------------------------------------
Command (m for help): t
Selected partition 1
Hex code (type L to list all codes): 7
Changed type of partition 'Linux' to 'HPFS/NTFS/exFAT'.
-------------------------------------------------------------------------------
Command (m for help): a
Selected partition 1
The bootable flag on partition 1 is enabled now.
-------------------------------------------------------------------------------
Command (m for help): p
Disk /dev/sdj: 1.9 GiB, 2058354688 bytes, 4020224 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x0003dd8d

Device     Boot Start     End Sectors  Size Id Type
/dev/sdj1  *     2048 4020223 4018176  1.9G  7 HPFS/NTFS/exFAT
-------------------------------------------------------------------------------
Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

Make sure you have sys-fs/ntfs3g installed.

Execute

mkntfs -Q /dev/sdj1

# mkntfs -Q /dev/sdj1
Cluster size has been automatically set to 4096 bytes.
Creating NTFS volume structures.
mkntfs completed successfully. Have a nice day.

Install boot sector

Make sure you have ms-sys installed.

Execute ms-sys -n /dev/sdj1

# ms-sys -n /dev/sdj1
NTFS Windows 7 boot record successfully written to /dev/sdj1

Now for the installation files.

Mount the downloaded ISO and the USB drive.

mount -o loop /$HOME/Downloads/Win10_1709_English_x64.iso /mnt/THIS
mount /dev/sdj1 /mnt/THIS

Now copy the files.

cp -Rv /mnt/THIS/* /run/media///

And that's it. Unmount the ISO/USB and go install.