Hey there,
Let's just start this off really easily by saying the obvious - I love you. You're probably laughing at how corny this is already but whatever, it's fine.
From a young age I remember that I wasn't too fond of you coming home at first. I refused to call you by your name and only referred to you as "baby" because I figured we were taking you back any day. However, you stayed and that's why we are the sisters that we are.
Thank God my parents didn't end up taking you back because there is no one else I would rather call my sister. Honestly, it was a tough time growing up because we fought probably every day and there was a point in time when I was worried we would never be able to be close friends like some siblings were. Thankfully, we are closer than ever and I'm too glad to call you my sister and friend. Our friendship has only gotten stronger over the years as we grew older which I am more than happy about.
I don't always tell you this but I am so incredibly proud of you and all that you have accomplished. I know it's always said that younger sisters look up to their older siblings but I have always looked up to you. For chasing after your dreams and never once doubting yourself or your abilities. I want to think that you learned that from me but I can only chalk up your morals and views to the way you have always viewed the world - you have always seen the world as so simple and in such a positive light.
Thank you for the constant laughs and for coming to my aid when I have been upset over pointless things that I honestly cannot even remember. Our friendship is so important to me and I cannot begin to express how thankful I am for you.
I am so protective of you and you might find that incredibly annoying but I just want to make sure that you live your whole life without any cares but also, please be safe. You are so adventurous and have such an amazing sense of adventure but I need you to remember that if anything were to happen to you, I would not be okay. I'm going to be selfish here and ask you to think of me before you do anything stupid. Please and thanks.
Lastly, remember that I am always here for you. No matter where life takes us, I will always come to your aid. It doesn't matter where we are both at. Your accomplishments are mine but your failures are also mine. Despite our occasional fights and harsh words, just know that they never erase how I feel about you. Thank you for being you.
You are forever my friend and sister.
Love you endlessly.