Intense
Violent, Fierce
い adjective
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of fierce and violent? Fierce and violent! That's intense.
What is fierce and violent? That old hag (はげ). Imagine her coming at you attacking you violently!
時々、夜になると激しい不安を感じるの。
Sometimes at night I feel an intense anxiety.
コウイチのダンスはいつも激しいです。
Koichi's dancing is always intense.