Unnamed Memory, Vol. 4 (manga)

With Tinasha heading back to her tower for a few days, Oscar is left without his guardian's supervision. Despite all her warnings to stay safe at home (nagging, if you ask him), Oscar ventures out of the castle to investigate a series of mysterious disappearances in a forest in eastern Farsas. There, he runs into his second witch-Lucrezia, the Witch of the Forbidden Forest! But is every witch as sweet and helpful as Tinasha...?