With some brainstorming, I created 3 ideas for a game. Then I decided on the central emotion I wanted players to experience (excitement). After that, I began thinking how other pieces of media captured this feeling, and one of the answers was gaming montages. That gave me the idea that I could synchronise the music to both a visual effect (screen fade) and a gameplay element (time speed) to capture the emotion. 

I looked at ways that other games made combat feel intense, and took them as inspiration for the abilities for my player character. Then, I started designing the enemies, in a way that makes players think strategically about how to deal with them.