Mythic items and heroics are such a classic combo in manga, and honestly, the best hunting ground for that specific itch isn’t one single place. For translated works, official apps like VIZ Manga or the Shonen Jump app are packed with titles where a legendary weapon or artifact kickstarts everything. 'Black Clover' comes to mind immediately with its five-leaf grimoire, and 'Dragon Ball' set the standard ages ago with the Dragon Balls themselves.
If you’re okay with fan translations while you wait for official releases, aggregator sites pop up in search results, but the quality can be a real gamble. Sometimes the translations for item names and lore get butchered. A lot of these stories also originate from web novels on sites like Shōsetsuka ni Narō, so the manga is often an adaptation. That’s how you get series like 'Mushoku Tensei' or 'The Rising of the Shield Hero'—the mythic item is right there in the title, driving the whole heroic (or sometimes anti-heroic) journey.