Summer Freyr

Weapon: Raydream Horn

Assist: Positional Assist

Special: Bonfire / Iceberg / Noontime

Passive A: Distant Counter

Passive B: Lull Atk/Def / A/D Near Trace

Passive C: Pulse Smoke / Preference

Sacred Seal: Mystic Boost / Def/Res Solo / Bracing Stance / Distant Def
 

• Summer Freyr plays very similarly to Duessel, as their prfs both grant them an incredible amount of bulk via their debilitating debuffs, and their stat spreads are very similar. 
• Summer Freyr’s Raydream Horn grants him automatic follow-up attacks while inflicting a -6 Attack buff on foes while buffing his own when initiating or as long as he has an ally within 2 spaces, and transforming allows him to inflict an additional -4 Attack and Defense against the foe while negating their follow-ups when initiating combat, giving him a strong presence on both phases.
• Freyr’s naturally high Defense and Resistance lend themselves well to stat based scaling specials such as Bonfire and Iceberg, although he can also opt for Noontime for in-combat healing.
• Distant Counter is a necessity for most enemy phase units as it allows them to counterattack ranged foes, which is vital in Aether Raids and extremely useful even outside of it. 
• Summer Freyr’s innate Lull Atk/Def is a great B slot option, debuffing the foe’s Attack and Defense and negating their Attack and Defense buffs. A/D Near Trace is also an excellent option that lets Freyr leverage his great movement with Canto, but at the time of writing is only available on Duo Catria(A seasonal locked 5*) and is thus difficult to obtain.
• Pulse Smoke grants Freyr some added protection from specials, Freyr’s C slot skill is mainly up to preference.
• If Freyr’s running a damage special, he’ll want the Mystic Boost sacred seal to ensure he has some source of healing, although if he’s teamed up with a healer in non AR gamemodes this isn’t necessary. Other than Mystic Boost, most stat boosting defensive sacred seals like Distant Def or Bracing Stance will get the job done.

Weapon: Raydream Horn

Assist: Positional Assist

Special: Bonfire / Iceberg / Galeforce

Passive A: Atk/Res Solo 3 or 4 / Death Blow 3 or 4

Passive B: A/D Near Trace / Lull Atk/Def

Passive C: Joint Drive Atk / Preference

Sacred Seal: Atk/Def Solo / Death Blow / Heavy Blade

• Summer Freyr is extremely capable as a player phase unit thanks to his exclusive weapon, giving him automatic follow-up attacks and a large amount of bulk via debuffs in addition to an impact-esque effect, meaning he has no trouble KO’ing foes while taking very little damage doing so.
• Stat based scaling specials such as Iceberg and Bonfire are Freyr’s best choice of damage special, but he can also opt for Galeforce alongside the Heavy Blade seal. Note that this is harder to use in Aether Raids, as Freyr’s weapon lacks any form of cooldown reduction and he has no access to cooldown reduction on his own, leaving him reliant on support units such as Velouria to get to a 2 cooldown Galeforce so he can reliably get his first activation off.
• Atk/Res Solo and Death Blow serve a similar purpose: Making Freyr hit harder. The choice between the two is mainly up to whether you want to deal with a positioning requirement or not.
• Freyr’s best B slot option for a Player Phase build is a Trace skill, as Canto allows him to function as an excellent hit and run attacker. Still, due to their rarity Lull Atk/Def is a fine substitute.
• Aside from Heavy Blade, the standard Attack boosting sacred seals such as Atk/Def Solo and Death Blow are great options. Not much more to be said than “more attack for existing is good”.