SummarySanseito, birthed on YouTube, makes election gains Party has also pledged tax cuts and welfare spending Leader says he wants to expand lower house presence TOKYO, July 21 (Reuters) - The fringe far-right Sanseito party emerged as one of the biggest winners in Japan's upper house election on Sunday, gaining support with warnings of a "silent invasion" of immigrants, and pledges for tax cuts and welfare spending.Birthed on YouTube during the COVID-19 pandemic spreading conspiracy theories about vaccinations and a cabal of global elites, the party broke into mainstream politics with its "Japanese First" campaign.The Reuters Daily Briefing newsletter provides...