What are the differences in blending philosophy between the Suntory Royal series and the Hibiki series?

That's an interesting question! Royal and Hibiki can be considered two flagship blended whiskies from Suntory, but their "personalities" are completely different. I'll try to explain it in simple terms.

You can imagine blended whisky as forming a band.

Hibiki - The Pursuit of a Perfect Symphony Orchestra

Core Philosophy: Harmony and Resonance (Harmony) The Japanese character "響" (Hibiki) itself means harmony and resonance. Its goal is not to make any single flavor particularly prominent, but to have all its components (various malt and grain whiskies from Yamazaki, Hakushu, and Chita distilleries) blend perfectly, creating a magnificent, complex, and flawless symphony.
Band Members: There are many members, and each is a master. You have Yamazaki's sherry cask fruitiness, Hakushu's fresh smokiness, Chita grain whisky's smooth sweetness, and so on.
The Blender's Role: Like a top conductor, their task is to precisely control the volume and position of each "instrument," allowing the sounds of violins (e.g., floral notes), cellos (e.g., woody notes), and flutes (e.g., fruity sweetness) to intertwine. Each is present in the other, ultimately forming a cohesive whole. When you taste Hibiki, you'll feel the flavors unfold layer by layer, incredibly smooth and elegant. It's hard to pick out one dominant flavor because they've become one.
In a nutshell: Hibiki's goal is to create an "ultimate balanced beauty"; it is a meticulously crafted work of art that pursues perfection.

Royal Series - More Like a Rock Band Led by a Star Vocalist

Core Philosophy: Heritage and Homage (Legacy) Royal's history predates Hibiki significantly. It was the last work personally blended by Suntory founder Shinjiro Torii, making it arguably the "origin" of Suntory's spirit. It was created to commemorate Suntory's 60th anniversary, so it inherently carries a classic, vintage vibe.
Band Members: This band has an absolute "lead vocalist" or "lead guitarist," which is the Yamazaki distillery's whisky, especially the magnificent sherry cask-aged whiskies. Other members (e.g., some whiskies from Hakushu and Chita) are more like excellent bassists and drummers. Their role is to provide a solid rhythm and support for the lead vocalist, making their voice more prominent and captivating.
The Blender's Role: Here, the blender is more like a golden producer. They clearly know that Yamazaki is the soul of the band, so everything they do is to maximize the iconic, sweet, and magnificent style of Yamazaki.
In a nutshell: Royal's goal is to "pay homage to classics." It unabashedly centers Yamazaki's charm, offering a more direct, richer flavor with a vintage, warm texture.

So, what's the fundamental difference?

Hibiki is "the whole is greater than the sum of its parts." It pursues an impeccable sense of harmony, where every component serves the team.
Royal is "the ace leads the whole." It has a clear core—Yamazaki—and other components exist to make that core shine even brighter.

To use an analogy, if you go to a high-end restaurant:

Hibiki is like a molecular gastronomy dish, where the chef uses dozens of ingredients and precise techniques to create a new, multi-layered, perfectly balanced flavor you've never experienced before.
Royal is like a top-grade M9 Wagyu beef, where the chef uses the simplest cooking methods, with just a bit of salt and pepper, allowing you to fully experience the outstanding quality of the beef itself.

Both are top-tier products, but they aim to deliver completely different experiences and emotions.