If you want to work as a composer on Kuni no Senso, then link a portfolio to any music you have written, be it a Soundcloud account, a YouTube playlist, a page on IMSLP, or whatever. The style I'd recommend sending in if you plan on working on the show is film scoring, classical, or some other form of orchestral music since that will be the primary style of the music in the series. 

NOTE: Most of the music done on this show is done through a musical notation software, so I recommend that, if you audition, you are either familiar with standard musical notation software like Muse Score or some sort of program like FL Studio