Creating a title character is not an easy thing to do, and avoiding a scenario in which these characters are only interesting because of their position as the series’ centerpiece is a daunting task.

This is not something Sandra Oh is unfamiliar with; “Grey’s Anatomy” presented a lead character whose storyline rather than personality did the heavy lifting in terms of garnering audience interest — and it allowed Oh’s performance as Cristina Yang to steal the show and viewers’ hearts.

What this proved was not that title characters cannot be interesting — instead, it proved that Oh was ready to be a series lead. And as Eve Polastri on BBC America’s “Killing Eve,” she is everything audiences could want in a drama series’ main character. Eve is a woman teetering on the brink of solace and destruction, of immense security and staggering danger. Her storylines throughout season one and two have been filled with convoluted emotions and sinister twists — and the characteristics that Oh has imbued in Eve throughout these beats have only further guided audience attraction to the character.

Especially in this past season, Oh has gifted Eve with the magnetic ability to be both cuttingly sharp and delightfully naive. Oh paints each of Eve’s investigative scenes as razor-focused and fast-paced. Manic, awkwardly steely and incredibly endearing, Eve demands immediate attention but maintains that attention by being so intrinsically human. She demonstrates her understanding of what is right and what isn’t, but quivers in between the two — a vulnerable uncertainty made viscerally vivid by Oh’s delicate mannerisms and delivery.

Eve is an undeniably compelling and beautifully crafted character in isolation. But where there is a hero, there must be a villain — and that is Jodie Comer’s Villanelle.

Oh depicts Eve’s need to capture the slick lavender haze that is Villanelle as feverish and frothing, and it seems obvious why she is so desperate: She is a British intelligence agent, it’s her job. But as the brilliant chemistry between Oh’s and Comer’s characters is egged on, and the stakes are leveled higher and higher, Eve’s desire to catch Villanelle becomes less about justice and more about curiosity.

Villanelle forces Eve into inescapably tight corners, and it is in those tight corners where Oh’s richest performances can be found. The manner in which Oh projects Eve’s sensuality and captivation with Villanelle is subtle and tart, leaving each scene with unspoken glances and softly spun voice breaks that audiences can latch onto and theorize over.

But it is also the way the pair co-opts each other’s ticks and behaviors that facilitates the women’s frenetic relationship. The effortless and casual, manic and feral paradox of the character Comer creates with Villanelle makes her the perfect center of Eve’s focus. The pair both play off of and concede to the other’s dynamic performances. Where Comer’s Villanelle functions so successfully because of the way she so expertly wrings vulnerability out of Oh’s Eve, Eve’s tenacity and ultimate denial of Villanelle’s means (and affection) is a direct symptom of the way the pair’s personalities infect each other.

For as much nuance as Comer brings to what could easily be a sociopathic stock character, at her core Villanelle is bereft of emotional attachment. The show’s first season incessantly inundates audiences with contradictory actions that posit Villanelle in a kind of unreadable space, her motivations never transparent. And because of this, “Killing Eve” strikes a complicated dichotomy between who Villanelle wants to be, and who she intrinsically is.

The ebb and flow that the characters create as they dance around each other in the most symphonic and unpredictable game of cat-and-mouse imaginable is a perfect and deadly cocktail. And as the series progresses, as Eve edges towards the loveable sociopath’s disposition, the resulting chaos is so intricately charged that season two’s finale intuitively concludes by busting the confines of that relationship wide open. Villanelle as the agent of that chaos — a role we see her execute constantly — but imbued with a new brand of agency that the hitwoman has not been privileged with thus far.

Season two’s subjugation of Villanelle to her handlers’ whims creates a pressure cooker — one which sees Comer’s subtle touches of Villanelle’s descent into rage as a revelation. And where the show had to this point framed Eve as the exception to Villanelle’s wrath, her impulsive retaliation hits a reset on the pair’s relationship, as well as the series as a whole.

That isn’t to say that, in her own convoluted way, Villanelle isn’t still steeped in affection for Eve — but rather, it’s the way that their relationship is chameleonic in meaning (for both of them) that asserts that the relationship is more utilitarian than it is unconditional.

All of this to say: It’s complicated.

To this end we see the pair’s relationship as less of a tragic romantic saga (sorry Villaneve shippers) and more as a battleground for power — and season two ends with Villanelle taking a huge victory.

To viewers’ pleasure, Comer and Oh never shy away from delivering the alchemical magic, born of skill and what sometimes feels like what must be pure luck, that it takes to breathe life into the characters. In their own right, both actresses are masterful, a tour de force. But together, their performances, well, kill.