How does Kase's language change from the first to the last letter?

In Kase's first letter, the language is formal and cautious, reflecting a sense of uncertainty and apprehension. As the letters progress, Kase's tone shifts to become more confident and assertive, indicating personal growth and a deeper understanding of the situation. By the last letter, the language is more direct and expressive, showcasing a greater emotional depth and clarity in Kase's thoughts and feelings. This evolution highlights Kase's journey towards self-assurance and resilience.