비가 오기만 하면 그 사람 생각이 나

The line, explained

Some memories have a trigger you cannot escape. For this narrator, it is rain: the moment it starts, that person comes back. Korean expresses this automatic, every-single-time link with -기만 하면, 'whenever… just', 'the moment… then'. It sounds a little helpless, which is exactly the mood of a film voice-over spoken to a rainy window. It is also very common in daily life, usually for funnier things, like falling asleep the second you lie down.

비 is rain, and 비가 marks it as the subject. Korean says rain 'comes': 비가 오다. So it is raining is 비가 와, and it rained is 비가 왔어. Snow works the same way: 눈이 오다. Here the verb 오다 takes the ending -기만 하면, giving 오기만 하면. The whole first half, 비가 오기만 하면, means 'if it so much as rains', 'whenever it rains'.

-기만 하면 is three small pieces. -기 turns the verb into a noun, 'raining'. 만 means only or just. 하면 is 'if (it) does'. So literally it is 'if it only does the raining', which becomes 'all it takes is rain, and then'. The ending attaches to any verb stem with no changes: 보기만 하면, whenever I see; 듣기만 하면, whenever I hear; 눕기만 하면, the moment I lie down. The second half of the sentence is the result that follows, reliably, every time.

그 사람 is 'that person'. 그 is that, for something both speakers know about, and 사람 is person. Korean films and songs use 그 사람 to talk about an ex or a lost love without saying the name, which keeps a little distance from the pain. 생각이 나 is 'comes to mind': 생각 is thought, and 나다 is to come up or arise. Notice the thought is the subject. You do not think of them; the thought of them simply arrives.

Read it slowly, like a voice-over: bi-ga o-gi-man ha-myeon, a pause for the rain, then geu sa-ram saeng-ga-gi na. Then change the trigger: 눈이 오기만 하면, whenever it snows; 밤이 되기만 하면, whenever night falls; 이 노래를 듣기만 하면, whenever I hear this song; 바다에 가기만 하면, whenever I go to the sea. Same memory, different weather. The ending is always -기만 하면, and the result always follows.