Roasting is applied after the tea is otherwise finished
This is the distinction most often missed. Fixation lasts minutes and exists to stop oxidation. Roasting lasts hours, often in several passes separated by weeks of rest, and is applied to leaf that is already made. The toasted note in a pan-fired green tea is a side effect of fixation; the toasted note in a Wuyi rock tea or a hojicha is the point of a separate step.
What the heat does
Sustained moderate heat drives off residual moisture and promotes browning reactions between sugars and amino acids in the leaf, generating compounds associated with toast, caramel, roasted nut and dark chocolate. It also softens astringency and thickens the perceived body, which is why heavily roasted teas read as smooth even when they are strong.
Level and rest both matter
A light roast leaves the underlying tea legible; a heavy one can dominate it entirely. Rest matters as much: a freshly roasted yancha can taste almost entirely of charcoal, and the same tea six months later is far more expressive. Roast character also fades over a year or two, which is why the same tea bought twice can seem like two different products.
Where it appears across the catalogue
Hojicha is green tea roasted until reddish-brown — a short hot roast that takes minutes rather than hours. Wuyi rock tea and traditional Tie Guan Yin use long charcoal roasting. Dong Ding and Hong Shui oolong sit in between. Liu An Gua Pian is a green tea finished over charcoal. Genmaicha is the outlier: its toasted note comes from added roasted rice rather than from roasting the leaf at all.