Kikkai-kun - Vol. 1 Ch. 5 - Darn you! Player Oh

[MangaDex]

 

[vigorousjammer]

Yes, this is obviously the true origin of the piloted mech suit.
The super baseball suit! lol.

In all honesty, if everyone's ready for a bit of a history lesson, while Mazinger Z popularized the piloted mech suit in 1972, it actually wasn't the first series to feature it.

The very first piloted mech suit was shown in the Golden Bat kamishibai way back in 1931, an enemy known as Dai Ningen Tanku or "Great Human Tank".

There was also a 1934 manga called Tank Tankuro by Gajo Sakamoto which wasn't exactly a piloted mech, but starred a round metal man who could transform into various shapes.

The first series which truly introduced the piloted mech as a main concept, however, where the protagonist is piloting the mech from the inside, is the 1948 manga, Genshi Ryoku Jinzo Ningen or "Atomic Powered Android" by Uno Kazumichi. The drawings are pretty cartoony and basic, but this was the absolute origin of not only piloted mechs, but also giant robots.

 

[NerimaShinjuku]

“There’s more to me than you’ll ever know/and I got more hits than Sadaharu Oh”