Tattoo sites are a dangerous way to look for Japanese words, mainly because most tattoos in "Japanese" are abysmal. Part of the main reason for this is that people who get kanji tattoos don't understand the language, so they figure a direct translation of their favorite phrase can consist of three or four kanji, and the results are ultimately illegible in Japanese. People also seem to be adverse to using kana, but insist they want Japanese. It's kind of like saying you want an English phrase but don't like consonants. Kanji are Chinese characters that were adopted into written Japanese, so there's a whole lot of overlap between the two.
Fortunately, you're talking about something that could be painted over if it gets screwed up. That said, if you you really want just three separate words not connected grammatically to each other, I'd have to say :
親切 (shinsetsu) for kindness. 思いやりがある is probably a more appropriate term for what you're asking about, but it's more of an adjectival phrase.
必要 (hitsuyō) for necessary
真実 (shinjitsu) for truth
That way you have three kanji compounds that express the concepts you're looking for.