A Chinese tattoo for your SOULMATE? 心灵伴侣 (xīnlíng -soul[=heart+spirit], bànlǚ -mate/partner/companion). Although this term is now used in Chinese, it might be of recent import from western influence. More often used (though perhaps not as evocatively metaphysical as "soulmate") is 终身伴侣 (zhōngshēn -lifelong[=end+body (thus mortal), bànlǚ -mate/partner/companion). It's still a beautiful Chinese idea, which is also very dear and familiar to our western vows: partners "'till death do us part..."