Spring Saleh

Weapon: Springy Axe+ (+Spd) / Ninja Masakari+ 

Assist: Positional Assist 

Special: Moonbow / Luna / Galeforce

Passive A: Atk/Spd Solo / Swift Sparrow 3 / Atk/Spd Catch / Life and Death 

Passive B: Lull Spd/Def / Hit and Run / Lull Atk/Spd / Lull Atk/Def

Passive C: Rouse Atk/Res / Joint Drive Atk / Hone Cavalry

Sacred Seal: Atk/Spd Solo / Heavy Blade / Life and Death / Swift Sparrow / Death Blow

• Saleh's extended range, great offensive stats, and nice offensive Axe options paves way for a more higher-investment offensive build. His default Springy Axe fortunately cuts down on costs as it's perfectly suited for the build thanks to its easy Atk/Spd +5 conditions as well as working flexibly both phases (which work perfectly with double Atk/Spd Solo in the A and Sacred Seal slots). For a more blitz-oriented build with better potential damage and higher hit count, Saleh may also consider Ninja Masakari, which is obtainable from Heroic Grails. 
• Many offensive A slots and Sacred Seals will do on this build; as mentioned, Solo skill in particular are preferred with Springy Axe due to working both phases. Ninja Masakari rolls well with just about anything, though Heavy Blade deserves special mention for activating Specials such as Moonbow and Galeforce very quickly with Masakari's consecutive-hitting nature. 
• A Lull skill of choice is a pretty obvious choice — preferably Defense-based to directly improve Saleh's damage output. Lacking those or preferring the hit and run approach, the skill literally called Hit and Run works wonderfully in tandem with Saleh's great movement and allows him to escape a space after a kill. 
• Saleh's C skill passive is less of a priority than other slots mentioned here, though Rouse Atk/Res comes by default on Saleh and is a nice option to improve his visible Attack as well as encourage Solo conditions. Joint Drive Atk actively improves Saleh's damage output even more in exchange for having allies nearby. On an all-cavalry setup, Hone Cavalry or other cavalry-exclusive C skills of your choice improves the performance of fellow horsemen. 

Weapon: Springy Axe (+Spd)

Assist: Positional Assist

Special: Moonbow / Iceberg / Luna

Passive A: Fury / Atk/Def Solo / Triangle Adept

Passive B: Desperation / Lancebreaker

Passive C: Rouse Atk/Res 

Sacred Seal: Swift Sparrow / Atk/Spd Solo / Atk/Def Solo / Spd/Def Solo

• Saleh hops in with a solid 37/36 offensive spread as well as a great default weapon in Springy Axe, which is possibly one of the best offensive Axe weapons at this time of writing. Specifically, it grants a pretty magnificent Atk/Spd +5 and handy penalty immunity if the enemy is above 75% — basically a given on the majority of content. It's not exactly difficult, then, to formulate a cheap and simple but effective attacker build.
• Everybody knows the song and dance of Fury + Desperation at this point: Fury improves Saleh's stats all-around, increasing his general offense and survivability cheaply. The recoil damage suffered after every round of combat contributes towards Desperation activation, allowing Saleh to make his follow-up attack immediately before a counterattack can do him in. 
  • For Assault modes (where you can only use one unit once), you can turn Saleh into a nice type check unit with Lancebreaker, helping him to totally turn the tides against most Lance enemies without Null Follow-Up. This can be paired with Triangle Adept to rub the salt in, though it pretty much limits Saleh to just attacking blue units. 
• With Spring Minerva being available as a 4-star focus in the same event, one may opt to inherit Atk/Def Solo from her. It's a fairly good A-slot skill as it grants more stats in Atk/Def and no recoil damage unlike Fury, and any bit of additional physical bulk helps out Saleh in the short run. It's easily pairable with Rouse Atk/Res — which also requires Saleh to maintain Solo conditions anyway — and any Solo skill of your choice in the Sacred Seal for a very high stat swing. 
• Moonbow works well enough as a short-cooldown Special, typically working no matter how long or short-lived Saleh's combat is. Luna gives better returns at a slightly slower turn rate, while Iceberg deals solid damage based off of Saleh's pretty decent Resistance stat.

Weapon: Plegian Axe+ (+Spd or +Res) / Deck Swabber (+Spd or +Res)

Assist: Positional Assist

Special: Noontime / Sol

Passive A: Distant Counter

Passive B: Lull Atk/Spd / Mystic Boost / Lull Atk/Def

Passive C: Atk Smoke / Rouse Atk/Res 

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

• This build pays better attention to Saleh's good Resistance (not super fantastic, mind you) for a melee cavalry unit, combined with great Attack and Speed and access to some rather great defensive Axe weapons. Of course, seeing as Saleh's defensive stats aren't the greatest at base, a high amount of investment in the form of merges, specific skills, Dragonflowers, summoner support, and support allies will be required to get full leverage out of this build. 
• Saleh will be choosing either Plegian Axe or Deck Swabber as his choice of weapon, and both are fortunately available from fellow Heroic Grail units. Both operate similarly between their solo conditions (i.e. being at least one space away from allies) and decreasing the enemy's Attack and Defense, allowing Saleh to hit harder and take hits with better ease. The difference lies in Plegian Axe's better potential stat swings if penalties are present on the enemy (which are easy enough to distribute with Atk Smoke, Sabotage skills, etc), as opposed to Deck Swabber cancelling visible enemy bonuses instead. 
• In both general gameplay and Aether Raids Offense play, Distant Counter will prove to be more useful than not as it allows Saleh to make good use of his invested defenses versus ranged enemies. He is also able to heal more often via Noontime or Sol as a result of being able to counterattack. 
• Saleh's cavalry class gives him fortunate access to Lull skills, which cancel out enemy bonuses in two stats and further applies an incombat debuff of -3 to said stats. For maximum survivability, Lull Atk/Spd directly impacts the offensive stats of enemy units, and the Speed swing isn't redundant with the Atk/Def effects of Plegian Axe and Deck Swabber. You may run Defense-based Lulls to improve Saleh's damage, though note they typically overlap with the Lull Def effect from Deck Swabber.
  • Alternatively, you may run Mystic Boost for reliable healing after every combat in addition to Noontime / Sol, and nerfing the damage from Wrathful Staff healers like Brave Veronica isn't a bad bonus.
• Atk Smoke is a very obvious option with the penalty magnification from Plegian Axe and is still a generally good defensive C slot nonetheless. To encourage solo conditions and/or if you already have penalty support from other allies, Saleh's base Rouse Atk/Res is good to keep. 
• As far as seals are concerned, Saleh will be wanting one of the Solo seals in order to further encourage the also-Solo conditions of either Axe. Spd/Res Solo is ideal as it further improves Saleh's magic tanking bulk as well as all-around Speed, though Atk/Spd Solo is optimal for improving overall offense instead while Spd/Def can be taken for physical improvement.