Like Ark, Ivy is a newbie Gate Guardian, joining only a month before he did, who is training under Jester. Because she became a member before him, Ivy believes herself to be better than Ark. Though she eventually comes to trust him, she still rags on Ark for silly things throughout the game.
There is little known about Ivy's past, just like with Ark. But unlike her partner, Ivy has a lot of mysteries surrounding her, kind of like most RPG heroines. Even though she's CIMA, Ivy has a pure desire to protect the lives of the fourteen pioneers. Because the Big Reveal happened right before the final battle, and everything that occurred as a result of said Reveal, there wasn't time to explain her motivation. Was she saved by humans in the past when mistaken for one? Does she have human foster parents? Or is there some organization of CIMA who wish to ally with humanity for some reason we don't know? Unless we get the sequel, all I can go on is variations of fan theories (mostly made by me since the other theories I've read concern main plot related questions).
While Ivy never says she has feelings for Ark--in fact, she says the opposite (not that something like that stops canon couples in many media)--there does seem to be a connection. Even when the two are ragging on one another, they slip in compliments here and there. During the time when Ivy was split from the group along with Rick, Philis and Yurald, she pulled the "I like him as a friend...but just a friend, you hear!" card after Philis called her on false harsh talk; if you emphasize the statement, it generally means you're trying to hide your feelings in pretty much any media under the sun. And then there was the ending, but due to how the Big Reveal went down you only see Ark's side of things.
Safe to say, at least for now, that Ivy is a serious contender for Ark's affection. Makes me feel sorry for Philis when she actually bought the "just friends" excuse after Ivy emphasized it.