Who else can be a guarantor?

Ifm a long term resident(1year) living in Japan 2 years. My grandfather is Japanese citizen but he lives in the Philippines. I want to bring my sister here with the same visa I have, so I applied her visa once , it was denied. According to the immigration, the guarantor which is me doesnft have enough money to support her(this was last year so I only been living in Japan for less than 2 years). They said that therefs no problem with the papers, the only problem was the guarantor. So I ask if who can be a guarantor, at the city office they said that only pr and citizen can be a guarantor. But I donft anyone whofs pr or citizen that can be a guarantor for her. Is there another way to get a guarantor?

whenever I renew my visa. My guarantor is only my uncle. his visa is child of Japanese but only for 3years. And I live in japan longer than him.

you already have an answer.
earn more money, pay taxes, and get an official document for your income, and re-apply.
why don't you do that ?

So you can use relatives as your guarantor? Uncles, Grandparents, cousins (all on the Japanese side of course)

What about friends, co-workers, bosses (if they agree)...this is in regards to extension of your visa (eg; spouse)