At the begining will appear a choice betwen Kaguya or Yuzuru. Pick which one you like, it doesn't trigger any route. Just use the Quick Save function to get both memories for the achievement.

Here is where you choose wich route you want do do.
But first watch the sub-characters events to get all memories.

1st - (Make her eat carrots.)

2nd - (Just stay quiet and carry her home.)

2nd - (Don't try it out.)

1st - Turn around.

2nd - Don't close my eyes.

2nd - Don't give up.

1st - (Take it seriously.)

2nd - (Something felt wrong.)

2nd - (I prefer the usual Yoshino.)

1st - (It looks great on you.)

2nd - (Rely on her.)

1st - (I'd have done the same.)

2nd - (Stop her.)

1st - (Not really...)

2nd - (That apology just now was better.)

2nd - Kaguya made it possible.

2nd - (Help Kaguya.)

1st - (I had fun.)

2nd - (Avert my eyes.)

2nd - (Pretend to be asleep.)

2nd - (I felt relieved.)

1st - (Hug.)

1st - (Hug her.)

2nd - (I'm angry.)

2nd - Why, is there something wrong?

2nd - (Leave)

2nd - (I'm still not sure.)

Route Trigger
Ren appears at the Shrine after completing at least 1 ending. But is not possible to trigger the Extra Route before completing all the other Spirits endings.
(Save here to easy access to the Extra Route.)
Each of this choices lead to this endings:
1st - (I want to go on a date with you.) -> Bad Ending
2nd - (I want to introduce you to everyone.) -> Normal Ending
3rd - (I want to break your restrains.) -> Bad Ending 2
For the extra route you'll only need to do the Normal Ending again. But on the 3rd wish you'll get a choice:
2nd - (I want to save you in the truest sense.)
Just watch all of them in any order you want.
2nd - Yeah...