If you came across mfn.yahooapis.jp and wondered if it's safe, the short answer is that there's not much to evaluate. This is a subdomain of Yahoo Japan's API infrastructure, and it currently serves a 404 page. That doesn't make it a scam, but it does mean the endpoint is either broken or no longer in use.
For an API subdomain, missing privacy policies and contact pages are normal — these aren't consumer-facing services. The SSL certificate and hosting are provided by Yahoo Japan, which adds a layer of legitimacy. However, the lack of any working content means you can't verify what this site was supposed to do. If you were expecting a working service or tool, look for an alternative. If you're just investigating the domain, the absence of a live site is a clear signal that this isn't an active web property right now.
In general, a 404 response from a subdomain of a known company is usually a dead endpoint rather than a phishing attempt. But without content, there's nothing to trust. If you need reliable access to Yahoo APIs, use the main yahooapis.jp domain directly.