Togainu No Chi was my first
BL game and I loved it! I have completed the entire game and got all the CGs and recollections. You should definitely play nano's route last in order to finish the game. To be honest, I was able to play his route with the walkthrough they posted:
Nano Ending
Choose: No, you can't stay
Choose: Turn around
Choose: Agree
Choose: Don't say anything
Choose: Who could he be?
Choose: Don't look away
Choose: Let it slide
Choose: ...Leave him be
Choose: Stick with Rin
Choose: Approach him
Choose: Taste it
In order to access this route and the choice: Approach Him,
you must have achieved ALL the endings:
Gunji Ending
Kiriwar Ending
Arbitro Ending
Keisuke Bad Ending 1
Keisuke Bad Ending 2
Keisuke Good Ending
Motomi Ending
Rin Ending
Shiki Bad Ending 1
Shiki Bad Ending 2
Shiki Good Ending
Hope I helped