You could technically do what you've asked, but if the "Windows PC" in your drawing has IP connectivity, then it would be more ideal to do what @rln mentioned and just Connect directly to the 2nd RaspberryPi running ser2net.
If for some reason it does not have IP connectivity, then yes, you could connect to the Raspberry Pi (pi-1) via serial cable (a UART serial cable directly, bluetooth via RFCOMM, etc) then have Pi-1 connect to Pi-2 via telnet (assuming ser2net is configured on Pi-2). You could also just SSH into pi-2 from pi-1 and use screen to attach directly to the serial port on pi-2 (I'm making the assumption that a USB to serial port adapter would be in use to connect to 'Device' at the far end). i.e. screen /dev/ttyUSB0 or picocom /dev/ttyUSB0
But if the Windows PC has IP connectivity and can reach Pi-2, then it makes more sense to interact directly with Pi-2 as @rln mentioned.
Shameless plug, for a project I recently posted to GitHub: https://github.com/Pack3tL0ss/ConsolePi
It's related, as it's primary function is to act as a serial console server (using ser2net). More info in the post I'm about to make in this forum.