Ok this is a very specific question, but I don't play league and really have no intention of (as most I've watched arcane and won't go farther than that) but are there any characters or skins the invoke a gundam-esc aesthetic?
Oh yes, quite a few actually.
There's the Mecha skin line for the obvious pick, albeit that is more explicitly based on Pacific Rim than Gundam. It's all about the champions being rendered as giant robots battling Kaiju in a near-modern sci-fi setting:
And then there's the Lancer skin line, which is now discontinued, which drew from Gundam aesthetics among other things, mixing it in with a nominally medieval tech-level setting where the mechs are seen as protector gods or destroyers of the world:
And finally there's Mecha Kingdoms, which sort of tried to combine the two previous skin lines. Like Mecha, it's centered around heroes using giant robots to fight horrible kaiju monsters and protect the world, and like Lancer it's set in a medieval fantasy setting, except this time it's a Wuxia-based world rather than European medieval:
I drew my two favourite Darkin as humans based on my interpretation of them in my head that goes on exclusively from Vibes. The noble and kind Aatrox and the playful ruffian rogue Rhaast.