Put in strictly Hollywood terms, Emiko Yamane is the love interest. She loves Ogata something fierce, but she's engaged to Serizawa.
Yep, we've got a classic love triangle here.
But…it's the most boring love triangle in movie history, isn't it? Emiko loves Ogata, and there's never a sense that she will be with Serizawa. She says she thinks of him as an "older brother" and that's basically their relationship throughout. Heck, Serizawa is so wrapped up in his work that we doubt he even knows they're engaged. Dude's wedding day would have taken him completely by surprise.
Angel in Da House
Instead, let's look at Emiko from a different angle. In many ways, she is an "angel in the house" character type. Halos and wings need not apply.
The angel in the house is a popular Victorian image of a proper woman. The phrase comes from a poem by Coventry Patmore, and the ideal expresses that women should be sympathetic, self-sacrificing, and a source of rejuvenating support for the men in her life. She should also keep her energies, activities, and thoughts concentrated on home life and moral purity (source).
Needless to say, the idea is a wee bit dated.
Quick disclaimer: the angel in the house isn't a Japanese concept. It's Victorian England to the core. As such, we're not saying that the filmmakers had this idea when conceiving of the character. We're just saying that the concept provides a useful context for exploring how this character relates to the other characters and the story. And always ask a doctor to see if angel in the house is right for your character.
And Emiko does show many of these character traits throughout the film. When her father, Professor Yamane, comes home from work, she has a beer at the ready and is intently worried when he becomes despondent at the thought of killing Godzilla. Also, when Yamane and Ogata argue over what should be done about Godzilla, she's notably silent. She certainly has an opinion on the matter, right?
Her angelness is perhaps most evident with Serizawa. She's the only person he shows his Oxygen Destroyer to, and she's obviously distressed at his fishy murder spree. However, she agrees to keep silent about what she's seen.
Why tell her in the first place, though? It's never explicitly said, but we believe that Serizawa needed to share the burden with someone. It was too much for him, and Emiko's supportive "angel of the house" personality made that possible. And she accepts that burden as though her duty.
She takes this duty to heart, too. She doesn't break her promise until Godzilla's attack on Tokyo. After seeing the death and destruction caused by the beast, she finally tells Ogata:
EMIKO:I can break my promise now with a clean conscience.
Yeah, ya think?
But Emiko's also a modern woman as well. She's part of the research team her father and Professor Tanabe put together to investigate Odo Island. Later in the film, she works at the field hospital, not as a nurse but by assisting Professor Tanabe's monitoring of radiation poisoning.
And here's the big one: she goes out on dates with Ogata without a chaperone and is also carrying out an illicit love affair behind her fiancé's back. Scandalous, we know. Certainly not the behavior of a house-bound angel.
In the end, Emiko's character makes sense for a 1950s female lead. She has one foot planted in the feminine ideals of the past, but she's also taking a step toward our consideration of a modern woman. She's more complex than an initial glance at her character arc may suggest. Certainly, more interesting than that boring love triangle. What a snooze.