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klavier being nervous about serenading apollo because serenading someone is more personal than singing at a concert for thousands of people, so he takes apollo to his apartment hoping it'll alleviate his anxiety.
cut to apollo and klavier at klavier's apartment and klavier's hands are shaking before he even strums the first chord and apollo has to help him relax but once klavier starts he's incapable of stopping and starts wondering why he ever had anxiety about it in the first place, because apollo's watching him with so much affection in his eyes and god why didn't he do this sooner, apollo's joining in now and klavier's the happiest he's been in years