I surrender is absolutly amazing !!! Ayumi, Akane, Kaede and Masaki's voices are perfect for this song so i wish the song would focus on them, but it's so nice to have a song where everyone get at least a line and not just the usual trio.
Koishite is... ok. Akane's voice is good for one line here and here, but when she get big part like that, she sound meh, IMO. But bonus point for giving most of the solo lines to someone else than the usual trio