The 1987 Japanese-exclusive Transformers series featuring characters with small robot heads is Transformers: The Headmasters, commonly shortened to Headmasters.
Takara produced the series after Japan chose not to import the American cartoon’s 1987 conclusion, “The Rebirth.” The Headmasters aired from July 3, 1987, to March 25, 1988, and continued the Japanese Generation 1 storyline with a full 35-episode series rather than a short concluding miniseries.
Its title refers to the Headmasters, small Cybertronians who connect to larger robot bodies called Transtectors. This differs from the Western version, in which Headmaster partnerships involve Transformers merging with organic beings from the planet Nebulos. That continuity difference is one of the series’ most distinctive features.
The other options are separate Japanese Transformers productions or concepts. Super-God Masterforce followed in 1988, Victory aired in 1989, and Zone was a 1990 direct-to-video OVA. Headmasters therefore identifies the specific 1987 series, not merely a character subgroup.