An early potential explanation was identified by Himuro in this post, picking up on a comment by Yu in a 2010 interview with 1up.com. Yu talked about his plans to emphasize on Ryo a "deeper dialog" with Shenhua in particular.
YS: This is not actually in the game, but as an example to give you an idea of what I mean by deeper dialogue, when Shenhua and Ryo are at home, Shenhua will ask Ryo if he would like to drink tea or coffee and the player will select one or the other. Or, Shenhua will ask Ryo a hypothetical question like: "There are four animals; a monkey, cat, dog and bird. You are crossing the river but you need to leave one behind. Which one will you leave behind?" And the player has to choose one. Shenhua will ask lots and lots of questions like these and the answers will get stored in the game and affect the outcome of the player's relationship with other characters. It's like a personality test.
After the Kickstarter was announced, more details were given on the first Twitch stream in June:
YS: With the Rapport System, various data on your interactions with Shenhua will be tracked, such as her level of trust and rapport with you and so on, according to your actions toward her and the way your conversations progress. Later, this will affect how cooperative Shenhua is toward you, for example. I think we’ll be able to express a new and exciting angle to Shenmue that wasn’t present in the previous games.
Twitter Q&A:
Q44: Since relationships between characters will be more prominent, will we see something like a multiple choice conversation system? A: I am thinking about dialogue selection system
Kickstarter countdown Twitch stream (link to video):
YS: This is also something I may not have described much in the Kickstarter project, but I'm thinking about a new form of cooperative exploration. It's a system that allows you to explore together with Shenhua. Well, you could say that Shenhua helps you. The way in which she helps you is determined by the Rapport System, which I think everyone has heard about before. As you carry out conversations with Shenhua, several parameters such as favorability, reliability and so on are tracked as you play. And as a result of building up conversations with Shenhua, whether she ends up becoming cooperative towards you, or gets upset with you, is something I'm planning to weave into the game.
Niconico interview:
Another factor this time is that more time will be spent together with Shenhua --although there will also be many new characters making an appearance --and so we will be introducing several new features to help portray the relationship between the two. The features include things like a new conversational choice system that occurs from time to time as well as a parameter that tracks the closeness of their friendship and there is also Character Perspective.
Summary:
- There will be an emphasis on deeper dialog, especially with Shenhua
- A new branching selection system for conversations will appear from time to time
- Several parameters will be tracked to measure Shenhua's attitude to you based on your replies, including aspects such as reliability, favorability, trust etc
- The level of rapport you have built up with Shenhua will effect how cooperative she is during your exploration together and so on.
I personally like the idea of a branching dialog system affecting the character interactions and potentially leading to multiple story variations. It should help add to replayability.