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Web services portal providing several services such as a search engine, web mail, news portal, business portal, page hosting services etc.
Most of the posts with this tag on Danbooru reference Yahoo! Japan, which began as a joint venture between Yahoo! and Softbank, but later became a separate entity when the parent company's core internet operations were bought out by Verizon Communications, but the purchase did not include Yahoo! Japan due to its continued popularity despite parent Yahoo's economic decline elsewhere. This explains Yahoo! Japan's longstanding use of the original red logo from before 2013, the year when Yahoo! itself started using a series of purple logos set into different fonts.
Yahoo! in both Japan and Taiwan has worked with several Virtual YouTubers: for the former, we have Virtual Wide; on the latter, via YahooTV, we have/had Hoonie Friends, Orith and Annin Miru.