Where the shape comes from
Two feet planted and turned outward, left and right splayed apart the way a climber braces before a step up. It carries 豆, a stemmed vessel, underfoot in 登, to ascend, to mount, to record, an old picture of feet placed either side of a raised stand or dais; and it tops the tenth heavenly stem, 癸, the last of the cycle, its own picture now hard to recover.
汉字 filed under 癶
No published character on HSK Guide is filed under this radical yet. 汉字库.