ツンデ令嬢立花天音とバカンス愛ランド～ジロジロ見すぎですわ！…子作りしたいんですの？恋人なんだから好きになさい！～

Protagonist Akito was a student who clashed daily with tsundere rich girl Ayane Tachibana.
One day he found himself the begrudging partner of her holiday trip.
She secretly had feelings for him, but would never say so directly.
Clumsily they confirmed the feelings were mutual, and the secluded beach was their paradise.

[From DLSite English]