Lieutenant Hikaru Sulu's duties as the U.S.S. Enterprise's helmsman took him, and the rest of the starship's crew, past the edge of the galaxy yet again on stardate 5221.3 (2269), when the Enterprise very nearly met her end in the hypergravitational field of the dead star known as Questar M-17, where the starship was nearly commandeered by a dangerous noncorporeal entity determined to force the Enterprise's crew to set it free so it could wreak havoc across the galaxy. On stardate 5554.4, on the newly discovered planet Phylos, the botanically minded Sulu almost died from exposure to toxins produced by an indigenous plant; fortunately, a Phylosian named Agmar administered an antidote in time to save the helmsman's life. Afterward, Sulu assisted Captain Kirk and Dr. McCoy in rescuing Commander Spock from the clutches of the misguided genetic engineer Dr. Stavos Keniclius 5 by using an expert judo throw against an attacking Phylosian plant creature.

On stardate 5577.7 (2269), Sulu suffered a compound leg fracture because of a fall from his helm console, after he and the rest of the Enterprise's crew had been shrunk to around a centimeter in height by spiroid radiation encountered near the adopted homeworld of the Terratins. On stardate 3183.3, Sulu, Dr. McCoy, and Lieutenant Uhura nearly froze to death in blizzard conditions created inside one of the Enterprise's recreation rooms, whose controls had been seized by a disembodied entity bent on performing a series of sometimes-deadly "practical jokes.? On stardate 6770.3, Sulu aged in reverse back to childhood, along with the rest of the Enterprise crew, as a consequence of the ship's accidental passage into a time-reversed antimatter universe. After the visiting Commodore Robert April brought the ship back home, a trip through the transporter, which retained all the crew members' original molecular pattern data, restored all the "children? aboard to their normal ages. Following the end of the Enterprise's pioneering five-year mission in 2269, Sulu received a promotion to the rank of lieutenant commander; he remained part of the starship's crew under Captain Willard Decker during the vessel's 18-month refit, and was present at the helm on stardate 7410.2 (2271) when Admiral James Kirk again assumed command during the V'Ger crisis.