0:00-0:50 Orchestral setup, gathered then emptied

• Pizzicato strings and a bright keyed figure set the pulse from the first bar; acoustic guitar (~0:13), light percussion (~0:19), and a flute lead (~0:39) enter in turn as the arrangement swells.
• Near 0:49 the build cuts away to a sparse beat — the intro hands over by emptying the frame rather than stopping.

0:50-1:30 The voice arrives as a murmur

• Over the thinned beat, IU enters near-spoken, quietly planting the confession — I love you, Oppa (~1:10) — with delicate chime notes answering around 1:11.
• Job: state the secret before any verse has to carry it.

1:31-2:40 Verse 1 narrows, then opens onto the first peak

• The sung verse takes shape ~1:31, the band settling in behind it ~1:37 as the sky-and-wind questions give way to the pretend-not-to-know lines (~1:54).
• The lift opens ~2:05 on the held-back-tears lines, brass accents joining as the melody soars to the what should I do? hook (~2:36). The English chorus is withheld; this first peak is the Korean hook alone.

2:40-3:55 Reload: verse 2 proves the same contract

• Verse 2 (~2:40-3:23) — the haircut, the outfit, more pretending — adds no new formal material; the repetition is the work.
• The second lift (~3:24-3:52) mirrors the first, then thins to a near-pause before the sighed what should I do, really (~3:53), a brief exhale that resets the frame.

3:55-4:38 Bridge shifts the address

• The voice turns outward — don't say such sad things — moving through smiling-through-tears images to pride folded away and the words she may never say again (~4:35), withholding the confession once more while loading the climax.

4:39-5:57 Payoff: high notes, the withheld chorus, the echo close

• ~4:39 the voice climbs three ascending notes at full belt, the top one held into ~4:59.
• After a quick count-in, the title chorus finally arrives from ~5:00 — make it a good day — the track's only full English chorus, carried to ~5:45.
• The band falls away ~5:50; strings ring out where the song began, decaying into silence by 5:57.