All Is One, One Is All

Izumi Curtis maroons Edward and Alphonse on Yock Island, the barren speck where she once dumped them for their apprenticeship, betting that isolation will help them recover a truth they have let slip. Winry watches helplessly as she, Izumi, and Sig sail back to the mainland. Trudging inland, the brothers notice how much has changed, since neither can swim in his altered body anymore.

Memories surface of the month-long trial Izumi and Mason once imposed, along with her parting riddle, the phrase that lends the episode its name, which they had to decode to earn her teaching. A masked stranger shadows the present-day pair, just as one tormented their younger selves. They reach the old sleeping spot where, years before, they puzzled over her meaning and first clashed with the intruder who drove them into hiding.

In the now, Al wades through shallow water to catch fish without harming his blood rune, echoing the training days when a fox stole the rabbit they hesitated to kill and clawed Ed's flesh-and-blood arm. Their campfire is scattered and their meal gone, marked only by a handprint; Ed proves it is a right hand and cannot be his, so they set off after the watcher. Flashbacks show the starving boys fashioning tools and dodging the masked man while inedible mushrooms left them hungry.

A past confrontation teaches Ed his lesson: seeing a dead cicada consumed, he grasps that his own body would one day break down and rejoin nature's larger current, and that alchemy flows with that cycle rather than above it, which was Izumi's answer all along. The brothers pass her old test. In the present, Ed connects the exercise to their reckless transmutation of their mother and resolves to press ahead. When Izumi returns with Mason, the stalker is revealed to be Mason himself, sent to guard them in secret, and a real boy steps from the brush as Edward eyes him with open hostility.

The episode draws on the manga chapters The Brothers' Secret, The Masked Man, and Knocking on Heaven's Door. The handprint gag carries an irony: because Wrath left it and Wrath holds Ed's original right arm, the print genuinely is Ed's own right hand.

Series director Seiji Mizushima felt the brothers had not truly absorbed the philosophy at that stage, given that they still went on to attempt human transmutation.