Brush pens give far more variation in line width than the usual fineliner pen. Their nibs have a wide foundation that then tapers to some good place. Commonly the nib is made from a conical bit of felt, but you will find pens that have a real brush tip https://stephenpcoyh.gynoblog.com/33503490/the-2-minute-rule-for-how-to-draw-with-ink-pens