Both Mori Ken and Hayashi Sakura had clearly no idea what just happened and why the playful atmosphere from earlier, thanks to Ken's wickedness, that is, suddenly shifted into a very, very serious one as Ken's body stiffened and his eyes went utterly still upon mentioning a fragment of what he is going through right now.
Surely for Ken, it is a topic that he avoids talking about with other people. But he found it so much relaxing to talk with Sakura about anything under the sun and so he was rather surprised within himself that he was able to mention that thing to her.
His past, his dark past, is not something that he wishes to delve into deeper, but maybe one day Ken could free himself from the harsh events that he faced as a child and that's when he could totally enjoy life himself.
But today is not yet the day for them to talk about it That is why… Ken was certainly doing everything that he could to totally banish it from his life for good.