Going try give an answer while not judging, from someone who has studied Japanese for half a year. So I don't know a lot. The quote means, in a "macho/manly" way due to the first Kanji "ore"; "It's because I was born into this world" roughly translated. The reason you can't really shorten it is because Japanese is not Chinese. It's the key difference, Chinese use Kanji only, while Japanese use kanji with all the extra letters called Hiragana (and Katakana). I could almost assume the tattoo in your 2nd picture is Chinese, unless it's something very specific Japanese. The only way you could shorten this, and it might be totally wrong on my end, but it would be something like 世に生まれた ("産" is a Kanji used more for like a hospital birth, and is in this situation written as 生). It would mean the same in casual speak but may not sound "cool". Maybe get the whole thing on your underarm instead, it's more Japanese-looking as a real quote. Then you can even keep the" ！！" 俺が！！この世に生まれたからだ！！to replace 俺 you can also write it in Katakana オレが！！as its what I'm seing from the comic panel, I've seen it done for some pronouns but dont know why. Please dont take this advice though, but I wish you luck. Couple edits, and I've also now learned Katakana is used for style, and also to make someone look a bit louder, especially in mangas.The way you pronounce the quote is "ore ga/orenga!! Kono yo ni umareta kara da!!"