|Legendary Ephraim is a bit of an unorthodox unit, encouraging a rather reckless playstyle. This build is geared to be a player phase melee duelist, and as long as Ephraim can activate his weapon's effect, he'll be able to duel with many opponents and come out on top. After all, he doesn't pick fights he can't win.
Weapon: Flame Siegmund is Ephraim's weapon of choice. It grants an Atk boost, boosting his already high Atk stat even higher, and it allows him to perform a follow up attack if there are more enemies near him than there are allies. While this does mean his positioning and his ally positioning is even more important, the pay off means that Ephraim can exchange blows and double his foes, making up for his rather below average Spd.
Assist: Reposition is a good Assist in general to use. Its uses are versatile, as it can either help bring an ally closer to the fray, or bring an ally out of danger. Cavalry units put it to great use with their high Mov.
Special: Luna is Ephraim's Special, which helps him break through sturdier opponents. His Heavy Blade Seal will help activate it on his second strike as long as blows were exchanged and nothing deterred Ephraim's Special charge. Should Ephraim use Desperation as his B skill, then Moonbow can work as his Special instead, giving up extra power for a faster charge. Galeforce is another very viable option. Ephraim's high Atk and high Mov means he'll able to activate Galeforce pretty quickly. With his extra turn, he can either choose engage against another enemy, or he could return to the safety of his allies.
A Passive: Death Blow 3 is a solid choice for Ephraim's A skill, granting him a +6 Atk buff when initiating combat. This will heighten Ephraim's Atk even further, which will help him overwhelm and overpower his opponents. Death Blow 4 however, should it be available to the player, is the superior option, giving +8 Atk instead. Alternatively, Atk/Def Solo 3 grants +6 Atk like Death Blow, but also +6 Def, and it works on either phase. All it requires is for Ephraim to not be next to an ally, but he's designed to be away from his allies anyway.
B Passive: Guard 3 is Ephraim's B skill, chosen to deter enemies from charging their Specials. In the heat of combat, he'll be exchanging blows with his foes, so this will be necessary to avoid being hit by an enemy Special during this time. Another option for Ephraim's B skill is Desperation 3, should Ephraim want to go more on the offensive. After Ephraim's taken some damage, this skill will allow his follow ups to occur consecutively, which can help him aim to defeat his foes before they can even counter.
C Passive: Atk Smoke 3 is an option for Ephraim's C skill. After he engages an opponent and destroys them, any nearby foe will suffer -7 Atk. This can make Heavy Blade 3 easier to activate, it can help mitigate some damage Ephraim may take on the enemy phase, like if he has to exchange blows. However, this skill slot is kind of flexible. Ephraim will have to be on his own, so buffing skills might not be the best choice for him, but it's still an option if he can buff his allies before riding into battle while they take care of business elsewhere. Other Smoke skills can work excellently with Ephraim however. Def Smoke 3 can help weaken nearby foes for him to break through, while Spd Smoke 3 may potentially save him from being doubled.
Sacred Seal: Heavy Blade 3 is necessary for this build to charge Ephraim's Specials much faster, letting him activate them in that round of combat. He should have no problem activating it thanks to his high Atk stat.