Rachel also continually challenges Bruce's motives and morals, a righteous tendency that director Christopher Nolan feels Holmes has the sophistication to deliver.
"She has this maturity beyond her years that the character really needed," says Nolan. "(Rachel) has to stand for a couple of things: the life (Bruce) might have had, what he's lost, but also the voice of his conscience, keeping him on his toes."
In one scene, when Bruce reveals his violent, half-baked plan to avenge his parents' murders, Rachel cuffs him twice on the head and tells him, "Your father would be ashamed of you."
"I don't think Rachel fears anything in this movie," explains Holmes, adding, "And I don't fear anything, so it works out."
"Batman Begins," however, is all about fear. Before taking up the cowl, Bruce Wayne must overcome his fear of bats, criminals and intimacy. It's just his bad luck to later meet the villainous psychiatrist Dr. Jonathan Crane (Cillian Murphy), whose alter ego is the frightening Scarecrow.
Crane's expertise -- and a makeshift mask made of holey burlap -- allows him to incite irrational terror in everyone, including Batman. Even the dauntless Holmes admits that Murphy's portrayal of Crane/Scarecrow got under her skin.
"He was creepy in the movie," Holmes says. "I didn't like that mask. I mean, I liked it, but it was creepy."
When a journalist points out that Murphy appears shorter than Holmes in the film, she laughs and holds up her hands and declares, "I didn't do it." At 5-foot-8, the former model is used to comments about her height and is even an inch taller -- without heels -- than boyfriend Tom Cruise.
Although Holmes isn't jumping up on couches as Cruise did on "Oprah" to express her rapture, she's not shy about sharing her feelings.
"I'm a very lucky woman," she says. "I'm really happy about my personal life -- totally in love."
Her co-star Michael Caine, who plays butler Alfred Pennyworth in the film, can attest to the Hollywood couple's affection. "They were kissing in the corridor," he reveals, making Holmes giggle.
"Batman" swoops into theaters Wednesday.