Tsuki wa Yamiyo ni Kakuru ga Gotoku

The rumor circulates that sometimes, in the dead of night, a white monster emerges. Legend has it that if you catch sight of it, you'll be consumed. One evening, Tetsu catches a glimpse of the man behind the monster's mask and resolves that this man is the one who will teach him swordsmanship and help him exact his revenge. However, the swordmaster Shino shows little interest in taking on any students. What must Tetsu do to achieve his revenge, and what events from Shino's past have shaped him into who he is today? Includes: Castilla --- Note: I've preserved the essence of your text while ensuring it remains in English and adheres to your instructions. The line breaks and structure have been adjusted for clarity.