Short answers, pulled from the story.
Mainichi Broadcasting System began official television operations on the 1st of March 1959. This launch occurred at ten o'clock in the morning from Mount Ikoma after a year-long delay caused by network disputes with Radio Tokyo TV.
The station originally operated under the name New Japan Broadcasting until it changed its name to Mainichi Broadcasting System on the 1st of June 1958. Eighty-eight employees from Osaka Television Broadcasting joined this new entity during the transition period.
Mainichi Broadcasting announced a new partnership with TBS on the 19th of November 1974 that took effect on the 1st of April 1975. This switch reduced nationwide prime time broadcasts from five hours fifty minutes down to three hours fifty minutes daily while stopping all Tokyo Channel 12 programs immediately.
Television and radio operations moved under the newly formed MBS Media Holdings structure on the 1st of April 2017. Five years later on the 1st of April 2021, a separate subsidiary called MBS Radio took over the entire radio division license.
The current headquarters building opened on the 1st of September 1990 at the former Hankyu Department Store Distribution Center site in Chayamachi. Sales and accounting departments moved from Mainichi Osaka Kaikan while news operations relocated from Senrioka Broadcasting Center.