Ai-chan!!!!
Nii-san misses you a lot you know! Seriously, you don't know how happy I am to receive your letter. I'm happy, really, really happy. I apologize if I sound like a kid, nii-san's a little tired you see. But don't worry, I won't die. Nii-san can handle it! But then, should I be thinner and paler than you when we meet, I probably need not worry too much about treating you to an all-around-the-world trip. I can probably afford that by then, but then, I'd probably look way older than my age too because of all the stress at work once I take over my father's business. Rich but tired. Can you imagine me wearing coat and tie? I seriously thought that I'd choke on it. But nii-san's all grown up now. I can't play around anymore. But again, don't worry. I'd live.
I wish to return to Hogwarts too Ai-chan. I would if I could. But I can't. I have to face it.But Ai-chan, I told you, didn't I? I'm always ready to help. Ill always be your brother. Blood kin or not, you're my younger sister, ne? And please, don't ever think that you're a burden. You can always tell me your worries. You can always write to me. In fact, I'd like it better if you continue writing your letters. I can't be there physically, but I want you to know that I won't abandon you. I probably sound overly dramatic, forgive your nii-san, ne?
P.S: Your way of writing is way better than mine
Ryuuji