I feel like it's not that weird they're not siblings and most of you guys commenting are either white/american or not used to asian culture because this is very common to call older guys brother. also brotherhood and sisterhood to those unrelated to you but are childhood friends is very common a lot of you are complaining when it's literally normal, you're just applying too much western logic into a manga which is literally asian.
I feel like it's not that weird they're not siblings and most of you guys commenting are either white/american or not used to asian culture because this is very common to call older guys brother. also brotherhood and sisterhood to those unrelated to you but are childhood friends is very common a lot of you are complaining when it's literally normal, you're just applying too much western logic into a manga which is literally asian.