harmony that binds the world

In my opinion, if it wasn't for Estelle then Brave Vesperia wouldn't have turned out the way it did. Estelle is the harmony that binds the group together. In the beginning Estelle was the one who insisted that they try out Karol's panacea bottle therapy to heal the Halure tree. This in turn gained Karol's trust and warmed him up to the team. Before that he simply wanted to travel with the group because he was scared of going through Quoi woods by himself. Karol was always shunned and ignored when he was in the Hunting Blades, being called a coward amongst other things. Yet, Estelle and Yuri trusted him and decided to follow on his words; even if the panacea bottle did not work they still tried.

If Estelle never existed then Rita would probably have not continued to accompany the team. First, she only joined the team to prove her innocence in the Aque Blastia scandal but after discovering Estelle's special power and how she was not using her blastia to heal she decided to join the group and investigate. Estelle was also Rita's first real friend. While everyone called her a freak for being so obsessed with her blastia research, Estelle supported her. Even when Rita acted coldly towards Estelle and the whole group Estelle insisted on talking to her and attempted to be her friend. Rita later warms up and even starts calling her Estelle instead of Estellise. She eventually starts to care a lot about Estelle and is the one who drives the whole group to saving her.

For Raven, it was his kidnapping of Estelle that made him change his ways and finally free himself from Alexeis's control. Because he kidnapped Estelle and brought him to Alexei, Yuri and the rest of the group had to fight him. It is there that he tells the truth and that he has waited for this day - the day that he is finally allowed to die, and get rid of his "wretched body". There, Yuri confronts him, telling him that he should continue living. It is there that Raven allows the party to escape, saving their lives. Afterwards, at Heracles, Raven rejoins but before rejoining Yuri suggests that his life belong to Brave Vesperia, meaning that whether he lives or not is dependant on the guild.

With Yuri, it is because he is friends with her that he insists on saving Estelle no matter what. He, along with Rita propelled the party, motivating them to continue their quest to save Estelle from Alexei's grasp.