The Lazy Writing at it's finest. A walk in the mountain ad they found the exact japanese ingredents he seeks.
BTW deaths by Amanita Muscaria are extremely rare, and there are various detoxifying methods, that also weakens the allucingenic effects. It was common to eat it in some region of Italy (Some regions called it "Il Malefico"/"The Malefic", but it's a popular and confusing definition as "Il Malefico" should stand for "Porcino/Boleto Maleifico", that is the "Boletus Satanas").
Some micologyst affirm the Amanita Muscaria should be classified as Edible, considering other shrooms that have detoxifying procedures are also classified as edible
LOL Fertilizer drops in dungeons. At least it isn't as extreme as that manga where everything, even food and money were dungeon drops.