highness, steps (of throne)
陛 centers on the idea of elevated status, specifically the raised steps leading to a throne, and by extension the highness or majesty of the person seated there.
陛 combines ⻖ (hill, mound) with 坒, which likely contributes the sound and the idea of steps or a raised platform. The character originally referred to the steps of a palace or throne, and later came to mean the emperor's highness.
The left side ⻖ suggests a hill or raised ground, and the right side 坒 looks like a set of steps. Picture the raised steps leading up to a throne, representing highness.
For ヘイ, imagine a guard at the throne steps saying 'Hey!' to stop unauthorized people: 'Hey!' -> ヘイ, and the steps lead to highness.
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Your Majesty; His Majesty; Her Majesty
His Majesty the Emperor
retired empress; ex-empress; former empress; empress emerita
retired emperor; ex-emperor; former emperor; emperor emeritus
their Majesties the Emperor and Empress
His Majesty the Emperor; the present emperor; the reigning emperor
His Majesty the King
Their Majesties the Emperor and Empress
Her Majesty the Queen
Her Majesty the Queen
Her Majesty the Empress
His Imperial Majesty; Your Imperial Majesty
Imperial guard