Mecha Gishi Resta no Daibouken

As a mechanical engineer thriving in Gearbolt — a city that runs on gears and gadgets — Resta Mechanity has it all figured out. Then the city's own guardian mechas start going haywire, tearing through the streets, and nobody knows why. Resta teams up with her childhood friend Krié to figure out what's causing the malfunction, and their investigation leads them to Frézero — a mysterious girl who somehow has a personal connection to Resta and an army of deadly robots at her command. This is an OVA from Studio Majin, based on a game, and it leans into that classic 80s-90s mecha OVA energy. If you grew up on stuff like Bubblegum Crisis or Megazone 23, this hits a similar vein — a compact sci-fi story with cool mecha designs, a female lead who actually builds things instead of just piloting them, and a mystery villain whose motives unfold gradually. There's a bit of that Neon Genesis Evangelion DNA too, in the sense that the threat feels personal rather than just "big robot smash city." The animation blends traditional and digital techniques in a way that gives the mecha sequences a distinct look, and the soundtrack does solid work keeping the tension up during fights. Fair warning though — this is tagged hentai, so adjust your expectations accordingly. But if you're into mecha action with some intrigue baked in, the core story actually has more going on than you'd expect from the genre label.