I think holy mantle would work better both in the literal way that he is wearing a mantle and in the metaphorical sense of taking on the mantle of hero
The other one you're probably thinking of is Orenchi ni Kita Onna Kishi to Inakagurashi Surukotoninatta Ken
How I Came to Live Out in the Country with a Female Knight Who Showed Up at My Place
I think it's a long the lines of they're not selling the potions they're just selling the liquid which on its own had no effect kind of along the same lines that during American prohibition grape Vineyards sold dehydrated grape bricks with instructions on how to not accidentally make wine