TOKYO — Nippon Steel was standing firm on its proposed $15 billion acquisition of U.S. Steel, Chief Executive Eiji Hashimoto said Tuesday after President Joe Biden’s blocked the top Japanese steelmaker’s move. “There is no reason or need to give up,” he told reporters at company headquarters in Tokyo. “We are convinced it’s clearly beneficial for both nations.” While acknowledging the effort may take time, he stressed the companies’ latest legal action in the U.S.