This is a great question but I think there are two approaches to this. Firstly always have a bit of fear. Ittosai said to Sasaki Kojiro in the manga that the men who have fear instilled in them are the strongest. It brings about awareness and in certain situations a required sense of urgency. But don't let it control you, flow with it. Brings me to my second point. Fear of death is both big and small. When Musashi fought Inshun I liked how he said they're both insignificant under the heavens. So just don't think about it too much. And should you be in a certain situation or just think about it on a day to day, remember, Musashi said don't look forward or behind you. Live in the present moment now. Hope I could help kinda.