My wife was doing the dishes, and I went over and stood next to her. Not to help, of course, because I despise doing dishes (though, yeah, I'd help if she asked).
Anyway, she was like, "Why are you standing there?" Which, in Japanese is:
なんで突っ立ってんの?
nande tsuttatten no?
突っ立つ (tsuttatsu) means "to stand around" or "to stand in one place doing nothing in particular."
Well, I had no idea why I was standing there, so I said (in English), "I'm just here for moral support."
She didn't know what "moral support" meant in English, and I didn't know the matching Japanese phrase, which, it turns out, is:
心の支え
kokoro no sasae
As you might have expected, they don't use this phrase in the same way that I said it, but you could use it more serious situations.
友達の存在はいつも私の心の支えになっている。
tomodachi no sonzai wa itsumo watashi no kokoro no sasae ni natteiru.
My friends are always there to lean on.
Okay, maybe that's not the best translation of all time. Translated directly (直訳すると), it'd be something like "My friends' existence is always there to support my heart."
As a side note, it'd be okay to switch out 心の (kokoro no), "heart's" (the way people use it in poems and love songs and whatnot) with 精神的な (seishinteki na), "mental; emotional".
So in the example above, it should be no problem to say:
友達の存在はいつも私の精神的な支えになっている。
tomodachi no sonzai wa itumo watashi no seishinteki na sasae ni natteiru.
My friends are always there to lean on.
What we've seen in this article so far is a good explanation of why literal translations can be problematic. People don't actually say the types of sentences listed above in everyday, casual Japanese.
Something that would have been natural to say to Rei in this situation is:
応援してる
ouen shiteru
I'm here for moral support. // I'm here to cheer you on.
A literal translation of this phrase would be something like "I'm rooting for you".
If you want to learn more natural ways to phrase things, you might want to check out NativShark. We provide context for our example sentences, so you know when they would actually be natural to say or write.
Good luck with your studies!
Niko