Vice Admiral Monkey D. Garp's offer to train Koby and Helmeppo references a supplemental story arc in the manga called "Diary of Koby-Meppo" where the pair of marine cadets struggle to find their place in the marine corps before earning the vice admiral's respect. Fortunately, and unfortunately, Garp the Fist's training regimen is as punishing as his previous pupils in the Netflix series must have claimed because it transforms the duo. Under his tutelage, Koby and Helmeppo grow into their own, though not without breaking first. The process often leaves Koby bloody and bruised, but he never gives up. Neither does Helmeppo, although he requires a little more encouragement than Koby to continue. In fairness, the change is best seen in Helmeppo, whose posture shifts dramatically from hunched to stalk-straight. He also changes his wretched mushroom haircut as part of his new look, so that's nice.
Garp's instruction sets them on a path for even greater change later. There's a two-year time skip in the manga and anime around chapter 600 or episode 500, respectively. In these two years, Koby earns the moniker Koby the Hero for his daring feats. Post-time skip, Koby is a Marine captain in SWORD, a special forces unit. He's taller, stronger, and more courageous than ever. He's still guided by a strong moral compass. Helmeppo did not rise as high as Koby, but he's now a lieutenant commander in SWORD. Wherever one goes, the other follows. They protect each other, and together, they protect everyone else.
