Made more intense after you learn the reason in episode twelve.
Chizuru: Is your scar... all right now?
Episode 11 in its entirety. The girls learning first hand what Ken does on a daily basis, appreciating what he does, standing up for him, going to his home to help him out when he is sick, and then a love confession.
Episode 4, when Minatsu becomes kinder and gentler through admitting (to herself) her love for Ken and then gives him her Sacred First Kiss much to his shock and surprise.
Episode 9: The Last Student Council Meeting. Ken honestly praises each of the girls' best qualities while saying that he loves all of them, after which all four girls whisper to each other and respond: