Route Diversion
Industrious readers have brought to my attention that this is a locked route. If you want to take the right branch, you'll have to have seen the true ending in Uzuki's route (the one where the ending theme, "Tabiji no Hate" plays). After that, you will see a dialogue box and hear Uzuki's voice asking you if you want to save the system data. Obviously, you want to pick "はい" and not "いいえ". If you have not fulfilled this condition, the game will automatically send you down the left route. As for which choices affect the route you take once its unlocked, please read below:
Way earlier in the story, in the scene titled "The Enju's Guidance," if you selected, "'Ah! No! Not Really!' and then leave,"
AND
If you chose not to tell Uzuki about meeting Kei in "The Dog and the Monkey," then you will be taking a left. You really should have a little more trust in people.
If you did NOT pick BOTH of those choices, you will be going right.