Quick Answer
Merc Storia: The Apathetic Boy and the Girl in a Bottle is streaming on Crunchyroll. 12 episodes (~5h total watch time). Availability may vary by region.

Where to Watch Merc Storia: The Apathetic Boy and the Girl in a Bottle
Merc Storia: The Apathetic Boy and the Girl in a Bottle is officially streaming on Crunchyroll. Availability depends on your region, so we've also listed search links for other major platforms below.
Confirmed Streaming Platforms
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Anime licensing changes by region. If Merc Storia: The Apathetic Boy and the Girl in a Bottleisn't on your usual service, try these.
About Merc Storia: The Apathetic Boy and the Girl in a Bottle
Merc Storia takes places in a world where humans and monsters coexist. The protagonist, Yuu, is a healer apprentice and possesses the ability to tame monsters. In a quest to regain the memories of Merc, a girl confined in a bottle, the pair embarks on a journey. (Source: MAL News)
Full details on MyAnimePulseFrequently Asked Questions
Where can I watch Merc Storia: The Apathetic Boy and the Girl in a Bottle legally?
Right now, Merc Storia: The Apathetic Boy and the Girl in a Bottle is on Crunchyroll. That said, anime licensing varies a lot by country — what's on Netflix in Japan might not be on Netflix in the US. If your go-to platform doesn't have it, try the other services listed above.
Is Merc Storia: The Apathetic Boy and the Girl in a Bottle on Netflix or Crunchyroll?
It's confirmed on Crunchyroll. Netflix availability depends on your region — some countries have it, others don't.
Is Merc Storia: The Apathetic Boy and the Girl in a Bottle available with an English dub?
Dub availability depends on the platform. Crunchyroll has been expanding their dubbed library a lot recently, and Funimation (now merged into Crunchyroll) historically had the biggest dub catalog. Check each platform's listing for Merc Storia: The Apathetic Boy and the Girl in a Bottle.
Can I watch Merc Storia: The Apathetic Boy and the Girl in a Bottle for free?
Crunchyroll offers a free ad-supported tier for some shows. Most other platforms require a subscription, but many offer free trials for new users. Tubi and Pluto TV occasionally have anime in their free rotation too.