Fix/Eliminate Japanese SEO Spam Attack in my website

I own shiningimage.com. It has decent traffic, and people constantly visit my website. When I google "site:shiningimage.com", a lot of japanese characters appear, and a lot of pages I haven't created. When I open them, it shows 404 error, so I can't even see what they have injected in my website. My livelihood depends on this website, and Google Ads. This is urgent, and I can't wait too much. My budget is not very big.