Elio would catch Zekrom, which would have much significance not only to him but to his family as a whole:

From an aesthetical standpoint, Elio's favorite color is black and his team is extremely melanistic - with secondary colors emphasizing the beauty of both the primary color and their respective patterns, and vice-versa, creating an unparalleled and mesmerizing palette. Additionally, the silver-haired trainer is quite familiar with futuristic settings as his home city of New Tork is one of the most technologically-advanced cities in the Pokemon world - being many centuries ahead of its time due to the profiting from the slew of positive effects of different space-time phenomena that commonly occurs within its vicinity. This is especially true after its overlay with Black City, which caused New Tork to evolve even further; the latter took on the aforementioned's color scheme and futuristic idiosyncrasies, while nighttime came earlier than expected in reference to Black City being cloaked in a beautiful starry veil of eternal night per its theme. The combination of "black" and "futuristic" - which is well-reflected in Zekrom's design, caused Elio to become enamored with the Pokemon for quite some time: wanting to make it his own.

From a cultural standpoint, Zekrom is one of Unova's most sacred legendaries; regarded as the "Deep Black Dragon of Ideals", it chooses those with an extremely strong and unwavering conviction to see their dreams and ideals come to fruition - no matter the cost, dubbing them the current era's "Hero of Ideals". Though he officially contracts with Zekrom as the current generation's "Hero of Ideals" (more specifically, its true body that's located in a separate dimension), which is later recognized nationally through a series of events relating to his #1 rival - who's coincidentally the current generation's "Hero of Truth", and thus explosively boosts the prestige of not only his family but his entire city, he hasn't officially captured it. He hopes that personally owning Zekrom would prove his might and skill as a high-level battler while "completing" New Tork's image post-Black City Overlay due to the latter and Zekrom being intertwined with each other; Black City is an extension of Zekrom, a physical manifestation of advancing towards one's ideals and the future. It's only right that such a Pokemon would guard and serve as a symbol for such a phantasmagorical city.

From a symbolic standpoint, in lieu of his pragmaticism, Elio's very much idealistic, and coming from a city that was partially built on the dreams and aspirations of both his grandfather and New Tork's generational residents, he saw it fitting that he would want to own a Pokemon that would best represent what the city was truly about and why it held its title as one of the most advanced locations in the entire world. Furthermore, while some of his aspirations are... relatively mundane and momentary, Elio's proven time and time again that he's willing to do whatever it takes to reach them; it's the same for everyone else in his home city. Though the residents reflect on the past, they typically use it as a foundation to decide and build toward their futures. Such dedication toward their ambitions and appropriate need for introspection plays a vital role in their respective string of successes over the years.