I also seem to be locked into the bad ending despite only doing Hifumi's events, although I never found a gym partner with her to trigger that event.
that gym partner event requires some of jun's events to be completed prior, as occaisionally routes will intersect, so you need to reach specific events with certain characters to unlock more for others
What about the second one where she runs off. Im about as lost as the main dude is on who to turn to
that one needs maya, i think up to maya's sixth event, though i may be wrong on what event though