Violet wants to become an Auto-Memory Doll because she wants to understand the meaning of "I love you," the last words she hears from her Major. Throughout the series and the movie, we learn that Violet became attached to the Major because he essentially raised her. Throughout the series, Violet encounters various forms of love: romantic love, sibling love, parent-child love, friendship love etc. However, it's not clear to me which love we are supposed to assume that Violet and Gilbert share. And whether or not it is even the same kind of love?
Haven't seen this series, but from r/VioletEvergarden FAQ here:
You are not the first; most people do. We encourage everyone first to watch the series (and read the novels) in order to come up with your own impressions of this relationship that lies at the heart of the series. If you have done that and are still confused, here briefly are some of the mods’ thoughts on the matter. For deeper dives into this complex relationship, please see the collections tab of this subreddit which contains several posts on the topic.
It is somewhat ironic that while Violet’s journey is a quest to understand Gilbert’s “I love you.” that same “I love you” confuses so many viewers of the anime. Some are quick to conclude (often based on a faulty understanding from the previous question) that Gilbert’s words are simply an expression of romantic love, which, given their relationship and ages at that moment, can be disturbing. Unfortunately, the tendency to categorize Gilbert's relationship to Violet as a solely romantic, and then treat Gilbert's dying words the same as a confession from some generic high school romance is quite common. That simplistic categorization may seem to make things easier to understand, but the series and movie (and novels) go to lengths to show his concern for her humanity and free will was primary. This love is something that defies simple categorization into standard categories of human relationships precisely because it was forged in unusual circumstances. Thus, Violet needs to learn what love is through encountering love in its manifold forms as an Auto Memory Doll.
That is how the atypical nature of Gilbert’s love synergizes with the series' episodic structure as Violet's exploration of various incarnations of love. Even Gilbert's word choice in Japanese makes his "I love you" clearly distinct from those romantic confessions as shown above. One can see romantic love as a part of this declaration of love, but to see their relationship solely in this light would be a mistake and a detriment to appreciating the show, which portrays the communication of love in its many forms.
For the anime and movies Kyoto Animation
chose to leave their relationship more ambiguous for a variety of reasons that can be speculated. This ambiguity shifts the focus onto Violet's growth in learning about the various types of love and allow examinations of guilt less prevalent in the novels.
The novels, on the other hand, by their nature
lend themselves toward making the internal dialogue of Gilbert clear to the reader. And following the conclusion of the second volume, it is unambiguously romantic.
My note: Lol you'd think 'on the other hand' would be in spoiler text.