Many of Valo's songs deal with themes of love. While talking about his songwriting, Valo stated: "I feel like there is no subject more important for a song than relationships. It's the only thing than moves me." He also takes some inspiration from literature, explaining: "As a guy who writes songs, I get excited about an idea, or a book, or a sentence. I don't necessarily get excited about the whole of Tolkien, I just get excited about Uruk-hai. Just a little detail that just makes my mind work overdrive." Valo and the rest of HIM referred to their music as "love metal", the idea of which was to combine more melodic and melancholic elements, with heavier influences. Valo has described HIM's music as "sentimental, hard-hitting rock". Some of Valo's favorite artists and musical influences include Black Sabbath, Type O Negative, Neil Young, The Sisters of Mercy, Fields of the Nephilim, Johnny Cash, Depeche Mode, Elvis Presley, Rauli "Badding" Somerjoki and Tapio Rautavaara. Some of his non-musical influences include Edgar Allan Poe, H.P. Lovecraft, Timo K. Mukka, Charles Baudelaire and Charles Bukowski, as well as Austin Osman Spare, Maya Deren and Shigeo Fukuda.