There's this music-box version of the opening theme that just stops you in your tracks. Utsuriginanakoi Tenki Ame is a 2007 Windows visual novel and its soundtrack "tournesol" is warm afternoon light turned into sound. "Morning Breeze" and "Sunlight in the Town" set up this gentle acoustic palette that makes you feel like you're walking to school in an anime.
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"Approaching Turbulences" brings in minor keys and tension without ever breaking the atmosphere completely. Each heroine gets her own theme and they actually sound distinct from each other, not just the same melody with different instruments.
"Serenade" is the quiet highlight, just strings and space. If you're into mid-2000s VN soundtracks with real personality in the character themes, give this a spin.