No operative System and twrp
The obvious solution to having no operating system is to add one. That's why what you can do, is to re-flash the custom ROM you are having, or a different one (maybe even a stock ROM). You can go on their page, and find your build there.

Once you download the ZIP, you put it on your SD, through the computer, and flash the ZIP from there, or you can use ADB to transfer the ZIP and flash.