に (cause/trigger of emotion)
grammar34 sentences
The particle に marking the cause, trigger, or stimulus of an emotional or physical reaction or change of state — 'at X,' 'by X,' 'upon X,' 'with X.' Common with verbs of feeling, sensation, and involuntary response: 知らせに驚く ('be surprised at the news'), 結果に喜ぶ ('be happy about the result'), 暑さに参る ('give in to the heat'), 酒に酔う ('get drunk on sake'), 喜びに震える ('tremble with joy'), 寒さに凍える ('be frozen by the cold'). Contrast the active-target に (target of action) where the subject is more agentive.