Risa Mizuno is a girl Takaki met in Tokyo. They met a couple of times due to their work and started going out after a while.
In the movie, Risa and Takaki were together for a while and Risa started sending text messages to him, inviting him to hang out, but Takaki did not reply back since he still has feelings for Akari.
(Source: xbobx, AkatsukiUlquiora; MAL)
