Roy

Weapon: Binding Blade (+Eff)

Assist: Positional Assist / Flexible

Special: Moonbow / Ignis / Sol / Noontime

Passive A: Atk/Def Unity / Sturdy Stance / Atk/Def Solo / Atk/Def Ideal

Passive B: Null Follow-Up / Lull Atk/Def / Mystic Boost

Passive C: Joint Drive Def / Atk Smoke / Def Smoke / Menace Skills / Flexible

Sacred Seal: Steady Breath / Atk/Def Solo / Mystic Boost / Sturdy Stance

• Binding Blade’s ample Defense/Resistance boost and innate Quick Riposte effect naturally lends the Young Lion to defensively-tuned playstyles, and the advent of Far Save helps him focus strictly on his melee match-ups to benefit from normal A skills without necessarily losing coverage. Increasing his Attack or Defense to improve his damage and physical bulk respectively are his best options. 
• Atk/Def Unity is a seriously powerful A skill that helps Roy absorb stat debuffs with impunity, reversing their effects entirely; it comes with the highest ceiling of all his options from a stat viewpoint but remains rather scarce. Alternatively, Roy can equip a fourth-tier Stance skill to prevent enemies from freely gathering enough Special charges to burst through his defenses — a helpful quality even when equipped with Null Follow-Up as his uninvested Speed is not all that reliable. One may also pick between other options like Atk/Def Solo and Atk/Def Ideal for pure stat boosts depending on preference between their varying conditionals. 
• For his B skill, Null Follow-Up shines to help mitigate damage against foes with automatic follow-up attacks and ensure that his innate Quick Riposte is not shut down by opposing Impact skills; overall, it’s a fairly useful asset that is sure to assist against common attackers. Lull Atk/Def is a somewhat weaker option whose usefulness varies on how often you actually run into visible buffs, and Mystic Boost provides constant post-combat healing though its other effects are functionally useless here. 
• Joint Drive skills are a common recommendation, though for good reason as they essentially provide stats for free — and in Roy’s case of an otherwise flat statline, such skills are more than welcome. Smokes are also useful when baiting multiple opponents in one Enemy Phase, with Menace skills being considerable upgrades provided you can get the positioning right. 
• The Steady Breath Sacred Seal is exceptional for the faster Special activation rate it provides; it can be leveraged for instant triggers on each counterattack with cooldown options like Moonbow, or more powerful choices like Ignis that would otherwise take too long to activate. If unnecessary (due to preference or if Summer Hilda / Brave Lucina support is available), any Sacred Seal that enhances Attack and/or Defense may be used. 

Weapon: Binding Blade (+Eff)

Assist: Positional Assist / Flexible

Special: Sol / Noontime

Passive A: Distant Counter 

Passive B: Null Follow-Up / Spurn / Null C-Disrupt

Passive C: Joint Drive Skills / Smoke Skills / Flexible

Sacred Seal: Atk/Spd Solo / Atk/Res Solo / Spd/Res Solo / Mystic Boost 

• Retaining his signature defensive focus, this build aims to maximize Roy’s balanced statline and infantry skill access to have him operate as the team’s main carry (i.e. an “omni”-tank). His choice of Asset is fairly versatile as a result — realistically, the best choice boils down to your preference and the type of support being provided to him — but those hoping to exploit damage reduction skills are more hard-locked into +SPD.
• Although not really an issue for general gameplay or in lower tiers of competitive modes, the loss of a stat-boosting A skill in exchange for Distant Counter is felt much more harshly in upper echelons— especially for someone like Roy who features a lukewarm overall statline at base. This makes incorporating a mix of high merges  Summoner Support, Dragonflowers, and his Resplendent if available alongside support from his allies pivotal for his success, particularly for Speed-based builds. 
• Roy has a few different options for his B skill:
  • Null Follow-Up is once again exemplary – and may be even more coveted here – to entirely shut down incoming threats with automatic follow-ups. Roy has no other way to impede the offensive performance of such foes, so this effect does wonders to safeguard his longevity (especially with the ubiquity of units like Valentine’s Lif who depend on such effects for their performance) while also supplementing his damage a little through guaranteed breakthroughs of Impacts.
  • Speed-based reduction skills like Spurn, Repel, and Close Call are fantastic for enhanced durability, decreasing the amount of damage he takes from opposing foes depending on how much faster he is than them. This scales up to a potent maximum of 40%, but the fact that Roy only has 31 Speed makes it prudent that one packs as many Speed boosts as possible. 
  • While not nearly as universally appreciated as the former two, Null C-Disrupt helps in case you have a particularly difficult time against units like Dazzling Staff or Firesweep Bow wielders; it may be possible to simply neutralize them during the Player Phase instead, but this may not always be a safe option.
• Healing Specials are a great way to bolster his survival via a consistent source of sustain, though do take caution if an opponent is equipped with Fatal Smoke on the opposing team. Noontime is recommended if access to accelerated cooldown support (e.g. Brave Lucina, Summer Hilda, New Year Velouria) is available, otherwise Sol tends to be more favorable. 
• Much of the same that could be said for Roy’s C skill in the first build applies here, with Joint Drive, Smoke, and Menace skills providing useful strengthening to his statline. Pulse Smoke is more notable here, though, for Aether Raids Offense depending on how often you run into teams centered on hastened Special activation mechanics, such as Infantry Pulse. 
• Sacred Seals that increase Roy’s key stats — though preferably in the form of a Solo skill — complement this build, but Mystic Boost is an interesting alternative stats for further counterplay to staves with an extra helping of healing.