I wouldn't be so sure of that. Considering Tsumugu's personality, he might see Hikari more of a key than a threat. With Hikari now here, Chisaki can't anymore keep herself unchanging with the excuse of waiting for Hikari. She will have to decide things for herself, one way or another. I believe that's why Tsumugu wanted them to meet; it would finally force Chisaki to do something. Of course it might also mean Tsumugu could lose, but he was slowly losing anyway, with both of them growing older but Chisaki's heart stuck frozen in the past.