What do i have to do to trigger mike romance route?
several things actually:
it's described in the guide posted in OP, copied in here:
Unofficial V.1.4 Walkthrough
Make these choices:
Day 1: in the elevator: Comment on the weather + meet him at the elevator
Day 7: at the cinema: Go and check if he’s ok
Day 11: at work: Give him hope
Day 12: at the restaurant, pick a costume online
Day 15: go to Mrs. Clarkson first thing in the morning, get stuck in elevator with Mike and then visit Mike the same day for Cosplay...
Day 17: read the guide. After completing scene 7, walk back home. She runs into Mike. Choose: Go to his place. Go there and choose: Find out how big Mike is... choosing Mike over Fred will trigger this event but also means you miss a Fred event - can't have it both ways
That's it.
One more thing: she need to have enough dirty whore level to trigger last event so make sure to make "good"
choices through out the game.