Summary
Ever since the start of the game,Honkai: Star Railhas been quite generous with the abilities that they give to free-to-play characters. These characters include all four stars since you’re able to get them at any point and various paths given to the Trailblazer, since you can unlock them through the story.
During the main story of Penacony, you get the third path for the Trailblazer in the form of Harmony. It’s one of the best units you’re able to have in the game, and it also introduces a new type of play style.

Combat Type
Fire
Asta has been a great support from the very start of Honkai: Star Rail, but her usefulness, unfortunately, goes down when compared to other Harmony units. However, apart from the SPD provided by her Ultimate, one of the best parts of her kit is the amount of Toughness Reducing damage she can deal.
Her Skill can hit up to five random enemies, dealing quite a significant Toughness damage with each hit. However, all this damage accumulates on one enemy if you’re fighting single-target bosses, which makes her Super Break DMG increase massively with the Harmony Trailblazer.

Wind
We can’t talk about characters who are great at shredding the enemy’s Toughness and not mention Sampo. His Skill can deal multiple instances of Wind DMG while the Ultimate deals one instance to each enemy. Both these attacks have some phenomenal Toughness-reducing abilities.
However, the best part about this synergy is that you may get quite a lot of value from Sampo if you build him with a ton of Break Effect, especially with certain Eidolons. This value increases even further with some phenomenal Super Break DMG from the Trailblazer.

Admittedly, Himeko isn’t the best character whencompared with other five-star units in the game, unless you’re looking at fighting Pure Fiction. However, it’s still impossible to ignore her talent, which allows her to perform a follow-up attack once you Weakness Break a certain number of enemies.
This directly synergizes with Harmony Trailblazer as you need to break enemy weaknesses to get value out of them. Furthermore, the best part bringing these two together is that Himeko’s follow-up can also trigger Super Break DMG, albeit not dealing a lot of damage.

Imaginary
Dan Heng: Imbibitor Lunae’s first release brought ripples in the world of Honkai: Star Rail as this character could do a lot more than any other unit in the game. While that’s not true anymore withDPS units like Acheron or Jingliu, he’s still a phenomenal damage dealer while having a ton of Toughness DMG as well.
When you use his Skill three times and use his Basic Attack, you’ll see some of the highest Toughness damage on the enemies. Moreover, he shares the combat type with Harmony Trailblazer, which opens up the path for special gear like the Penacony ornament set.

Ice
With the next few entries, starting with Misha, you’ll quickly realize how various four-star characters are some of the best pairs with Harmony Trailblazer in the current state of the game. The main thing you’ll be using here is Misha’s Ultimate, which can deal up to ten random hits on the enemies.
Each hit has a respectable Toughness damage, which can also be increased with certain other characters. While it’s difficult to get a lot of value from Misha himself, you can use this high Toughness damage against single-target enemies to get massive Super Break DMG.

Fromone Ice character to another, it’s almost impossible to not see the synergy between Harmony Trailblazer and Ruan Mei. The former needs to break the enemy’s Weakness and scales their damage based on the Toughness reduction on the enemies, while the latter directly doubles the Toughness-reducing damage dealt by your characters.
However, even though these two Harmony units go really well together, you still won’t be seeing a lot of Super Break DMG from Ruan Mei herself since her Basic Attack doesn’t have high Toughness damage. You’ll have to pair them with a couple of Toughness-based units.

Quantum
Speaking of units that are based around the enemy’s Toughness, Xueyi is the best DPS character you can use alongside Harmony Trailblazer with the current roster of the game. The main reason behind this is her ability to reduce the enemy’s Toughness regardless of their weaknesses in some instances.
She also gets a direct DMG boost from her Break Effect, which makes the stat one of the best for her. Combined with Imaginary Trailblazer, you’ll find Xueyi dealing a ton of damage every time she gets a turn.

No matter what team you’re using in Honkai: Star Rail, you will always need a sustainer to keep everyone alive due to the turn-based nature of the combat. Surprisingly, for Harmony Trailblazer, the best sustainer you can have is a four-star unit hailing from Penacony itself.
Apart from having respectable healing from his abilities, Gallagher buffs his Basic Attack once after using his Ultimate. This Basic Attack enjoys high Toughness damage and Break Effect, which makes it perfect to get the kind of damage numbers that you’ll never see on a sustainer.