Young Boyd

Assets/Flaws: +SPD or +ATK

Weapon: Large War Axe

Assist: Positional Assist

Special: Glimmer / Draconic Aura / Moonbow / Luna

Passive A: Surge Sparrow / Swift Sparrow / Atk/Spd Push 4 / Atk/Spd Ideal 3 or 4 / Misc. Atk/Spd A-Slot skills 

Passive B: Null Follow-Up / Lull Spd/Def / Spd/Def Tempo / Hit-and-Run / Desperation

Passive C: Odd Tempest / Infantry Pulse / Time's Pulse / Various Joint Drives and Menaces

Sacred Seal: Flashing Blade / Heavy Blade / Fury / Blade Session / Atk/Spd Solo / Swift Sparrow

• Large War Axe's dedicated Atk/Spd focus and effects, as well as Boyd's skewed statline towards said stats, makes him a perfect candidate for an all-out attacking setup. 
• The setup and premise are simple: 
  • Stack Boyd's offenses as high as you can with any initiation-friendly, quality Atk/Spd passives you can offer in his A-slot and Sacred Seal, unless you are running Flashing or Heavy Blade in either slot to quicken the frequency of his Specials.
  • Run a 2 or 3 CD Special for reasonably-timed burst damage — Glimmer and Draconic Aura are usually pretty great due to Boyd's usually super-stacked Atk, while Moonbow and Luna rewards almost equally well with better results against high Def enemies. 
  • Finish off with a fitting B-slot skill. 
    • Null Follow-Up is most universally useful on account of many dangerous units relying on guarunteed follow-up skills nowadays. 
    • Lacking that, Lull Spd/Def and Spd/Def Tempo primes Ross — er, Boyd's — damage and follow-up potential pretty well with good secondary effects of their own. The choice between enemy bonus cancellation and anti-Guard, respectively, is up to you.
    • For lower-rarity options, Hit-and-Run gives Boyd the option of stepping back a space after battle (copium Canto, so to speak), and Desperation leverages all that nice Spd investment by allowing Boyd to make his follow-up immediately after some HP setup.
  • Boyd's C-slot is mostly flexible and can simply be left to his default Infantry Pulse, but if you're able to offer some arguably optimal choices, Odd Tempest specifically works well with Large War Axe's lopsided performance boost on odd-numbered turns, and Time's Pulse is generally good for faster-going Specials. Miscellaneously, Joint Drive Spd, Joint Drive Atk, and most Menace skills involving said stats are just as fantastic. 
• Since this is mostly a collective selection of skills, some comprehensive combinations are as follows and can be modified or combined to your liking: 
  • Sustainable Initiator: Surge Sparrow + Heavy Blade or Flashing Blade + Lull Spd/Def or Spd/Def Tempo + Draconic Aura + Time's Pulse
  • Ideal + Menace Debuffer: Atk/Spd Ideal + Atk/Spd or Atk/Def Menace
  • All-Out Offense: Atk/Spd A slot + Atk/Spd Sacred Seal + Lull Spd/Def

Assets/Flaws: +SPD

Weapon: Large War Axe

Assist: Positional Assist

Special: Vital Astra / Noontime / Glimmer

Passive A: Atk/Spd Solo / Atk/Spd Ideal 4 / Distant Dart / Distant Pressure

Passive B: Frenzy / Spurn / Close Call / Repel

Passive C: Joint Drive Spd / Odd Tempest / Infantry Pulse / Atk/Spd Menace

Sacred Seal: Atk/Spd Solo / Darting Breath / Spd/Res Solo / Spd/Def Solo

• Boyd can venture the path of the sword and run a moderately effective speedster build. In essence, simply build up his Spd as much as possible through his passive skill slots to increase his follow-up potential and the damage reduction potency of his chosen Dodge skill (that is, Frenzy, Spurn, Close Call, or Repel). Overall, a build that prioritizes survivability yet maintains Boyd's natural offensive essence, all while making him less likely to choke on even-numbered turns.
• If you must run a Distant Countering A-slot, it's typically better to hold off until you can inherit a Spd-increasing variant — that is, Distant Dart and Pressure — as Boyd's Speed pretty much needs all the stacking it can get from its default value. Likewise, the same rule goes for every other passive you consider: more Spd or bust. 
• Due to a lack of cooldown acceleration present on Large War Axe, Boyd tends to prefer 2 CD Specials for frequent firing. Vital Astra rewards all the Speed investment in the build by offering additional damage reduction (assuming it's ready against an enemy hit) as well as Spd-based burst damage. Lacking that, more cheaper and conventional alternatives like Noontime for healing and Glimmer for larger retaliations should fare fine. It's recommended these skills be accompanied with a Breath skill present — preferably through the Darting Breath Sacred Seal or outsourced through other allies like Thórr's Worldbreaker.

Assets/Flaws: +ATK

Weapon: Large War Axe

Assist: Flexible

Special: Glimmer / Vital Astra

Passive A: Fury / Atk/Spd Push 4 / Distant Storm / Death Blow / Other Atk Boosting A-slot skills

Passive B: Wrath / Special Spiral

Passive C: Time's Pulse / Joint Drive Atk

Sacred Seal: Fury 3 / Quickened Pulse / Breath skills / Atk/Spd Solo

• This build plays more specifically to Boyd's one-shot-leaning strengths due to the sheer amount of damage Large War Axe allows him to deal, especially on odd-numbered turns. A good way of building on this is through constant Special trigger, giving Boyd increased burst damage at a moment's notice.
• Due to Large War Axe's lack of cooldown acceleration effects and Boyd's hardly reliable defensive strengths (unlike other extremely Def-heavy units, he can't really be counted on to run a pure physical Enemy Phase build with just 31 Def), our Special choices are a bit limited:
  • Glimmer is extremely accessible and ideal for one-shot kills. It scales greatly with Boyd's high Atk combined with Large War Axe, which naturally leaves dents in most targets except the most physically defensive — many of which are also handled by the true damage effect in the weapon (15% of Boyd's total Atk).
  • Vital Astra is the only 2 CD inheritable skill that scales off of its user's own stats at this time of writing. Though it's very rare and expensive, it gives some pretty reasonable returns on investment: increased burst based 30% of Boyd's total Speed (so Boyd doesn't falter versus high Def enemies) as well as up to 30% Spd-based damage reduction on enemy hits. Be sure on planning some maximal Speed investment to make this count, as it's totally possible for Glimmer to outdamage against some units regardless.
• On a Special trigger-based build, we look mainly at two B-slot options:
  • When Boyd's HP gets under 75% HP (which is doable by taking skills such as Atk/Spd Push or Fury in the A and Sacred Seal slots), Wrath rewards this with an additional +10 damage to Boyd's Special triggers. Additionally, it allows him to ready up his chosen Special at the start of every turn combined with Time's Pulse. 
  • Special Spiral is a more immediate charging method; unlike Wrath, it cuts cooldown after each successful battle where Boyd survives and his Special triggers. For those that don't appreciate the "wait-and-see" approach of Wrath, Special Spiral should suffice. To charge it up effectively:
    • Use Pulse skills through Time's Pulse, Quickened Pulse, or outsourced substitutions like Infantry Pulse.
    • Handle one combat with a Breath skill active in the Sacred Seal or through other allies.
• Laconically, effective skill combinations are as follows and modifiable:
  • Charge-and-wait Wrath: Fury OR Atk/Spd Push + Wrath + Time's Pulse + Fury (Sacred Seal)
  • Self-charge Spiral: Special Spiral + Time's Pulse + Quickened Pulse (Sacred Seal) 
  • Vital Astra Spiral Spam: Vital Astra + Atk/Spd Boosting A-slot + Special Spiral + Darting Breath or Atk/Spd Boosting Sacred Seal
  • Vital Astra Wrath Spam: Same as above, but with Wrath and Time's Pulse. 

Weapon: Large War Axe

Assist: Rally Assist / Flexible

Special: Moonbow / 500 SP Special (for Arena Scoring)

Passive A: HP/Atk 2 / HP +5 / G Duel Infantry 3 or 4 (for extremely specific Arena use only)

Passive B: Even Pulse Tie / Sudden Panic / Various Ruse skills

Passive C: Infantry Pulse

Sacred Seal: Panic Ploy / HP/Atk 2

• Bartre is honestly a cheaper choice for this, but if you need to put Boyd to work immediately, his unusually high HP and default skill in Infantry Pulse (already a good skill that quickly charges the Specials of fellow infantry units) makes him a natural team player in the art of HP stacking support. Keeping Large War Axe's offensive boosts in mind, Boyd can still occasionally lend a reasonable heavy-hitting hand when needed.
• To increase the success rate of Infantry Pulse and other skills listed here, building up Boyd's HP is a pretty clear choice here.
  • For Assets/Flaws, going for +HP or maintaining a neutral statline (to save on Trait Fruit) will do for the most part. 
  • HP-increasing passives such as HP +5 or HP/Atk 2 is a pretty easy way of achieving a high HP threshold. For Arena use ONLY, you may consider G Duel Infantry as they count as 300 SP skills, unlike the normal HP skill family. Note that their built-in BST is pretty much made redundant with Boyd's naturally high bin of 185 and this should only be done if you want to make him a debuff bot in Arena. In this same context, you'll want to consider a +ATK Asset only as that launches Boyd into the next scoring bin of 185.
  • You can run an HP passive in Boyd's Sacred Seal as well, though it fights with Panic Ploy as a potential choice to widen Boyd's supportive versatility.
• Boyd's B-slot skill further extends the amount of support he can lend. 
  • Specifically with all the HP investment, Even Pulse Tie (which shuts down dangerous fully-charged skills such as Life Unending and Ice Mirror) and Sudden Panic (which applies Panic to grouped-up enemies with lower-HP) become great choices.
  • Running a Rally assist also means a Ruse skill is a potent and more proactive option; Boyd can power up allies with stat bonuses while applying stat and 【Guard】debuffs to enemies within columns of your choice.