A-Raiyuu, Storm's Edge
The extra combat step is the reward, but the design's whole weight rests on a single word: alone. The payoff only fires when your Samurai or Warrior swings by itself, which means the deckbuilding puzzle is inverted from the usual go-wide instinct. You cannot flood the board and take two turns of combat at once; the tension is exactly that a lone attacker is the most gang-blockable thing on the table, so you have to make one champion big and evasive enough that it gets through and gets through twice. That constraint is what keeps the double-combat engine from collapsing into a mass-alpha-strike blowout. The untap clause is the connective tissue: your first-striking threat crashes in, refreshes, swings again in the bonus phase, and still stays untapped to guard on the opponent's turn. The ceiling is narrow by intent, too. The second combat is gated to the first combat phase of the turn, so you get one extra phase, not an infinite loop off repeated triggers. This is the aggressive, single-champion face for the Samurai mechanic that Kamigawa's lineage had long circled, where lone-attacker bonuses and modified-creature payoffs kept implying a commander built to send one huge threat in twice. The four-mana first-striking body delivers on that promise without demanding a combo: strap on a sword, suit up your one attacker, and let the extra phase do the arithmetic.
