It seems in most of these harem mangas two things usually happens: 1) the childhood friend tends to lose and 2) the first girl to force a confession showdown situation that requires the male to answer tends to lose. Looks like one of the losers just forced her situation to the front.
Takamine may not be the only one with a supernatural ability, this new girl may have one that can maybe either neutralize, compete, or identical to it, this is the only way I can see where she could be any kind of competition, threat, rival, etc to her. It may also be why she flashed him.
He's thrown a ton of hints at her like bricks at a riot... she still hasn't a clue. She's going to need someone to tell her directly whether that person is Runa or not.
He has never directly said it to her and it seems obvious she won't figure it out... his clue in life is that she rides the short yellow bus wearing a padded helmet
I don't even think that would matter because Jirou is the master of cuck-fu. Akari will win since she's not skilled in defensive martial arts of "childhood-friend".
At first I felt this was going to be one of those filler arcs delaying the inevitable by dragging in the gyaru trope but I wish the author, editor, and this company has the BALLS to demote Amano to a second level tier character that she should have been all along.