Avatar:
Hoshido characters seem to focus exclusively on offense. It makes sense to make the Avatar defensively minded, so I made him a knight. He should pick up Pavise and replicate to provide good coverage for the team. He could marry Scarlet and also grab rally defense to further boost his role as a defensive unit. Armored Blow and Luna are both good, of course.
Azura (Support):
Kinshi Knight (for Amaterasu), A+ Sakura, Priestess (for Renewal).
Felicia (Support):
Middling. Can only A+ Hana, and grab life and death to boost her weak offensive options, but this makes her vulnerable too.
Jakob:
I hate Jakob as a character and he is once again middling but in Hoshido mode his class sets are fairly unique and useful. Takumi is the only friendship set that makes sense for Jakob.
Kaze (Offense):
Whereas Kaze was one of the only ninja in Nohr mode, he is but one of many here. Kaze has excellent skill and amazing speed, ok strength and res, but terrible luck and defense. A+ Silas (only reasonable choice) and Kaze has access to a great deal of powerful skill-activated abilities. Luna is perhaps most useful to cover his middling strength growth. Life and Death, Replicate, Astra, Lethality are all good choices, along with the faire skills. He should probably only take one of the two faire skills given how many good options he has, and stick with that.
Silas (???):
Silas is now one of only a handful of cavaliers, and the only one that can pass down the cavalier class. He is a solid unit with no weaknesses outside of a poor res growth. He has no great strengths either, though, so it’s hard to put him in any category until his stats have grown more. Great Knight, Hero, and Paladin are good, but avoid Bow Knight: few enemies use shurikens in Birthright so shuriken breaker is not useful.
Mozu (offense):
All of Mozu’s classes are good and she could benefit from being in any of them. Her only A+ option is Oboro which gives her yet more broad options. Get reclassing!
Shura:
Skip. Weak classes aside from ninja, which you have a lot of. Terrible stats also.
Izana:
Skip. While Izana was the only Onmyoji in Conquest, he’s not here, and offers nothing new to the table. Izana would have offensive potential but he’s marred by his low starting mag and his limited growth potential.
Ryoma (offense):
Ryoma has a strong mix of nearly every stat minus resistance, magic and defense. All of his classes offer him something good. His superior skill makes Silas a good A+ option, who gives him Aegis and Luna.
Hinoka (offense):
Hinoka's got deadly potential due to her spear options and her movement. She's fairly solid in most categories but has poor def and middling hp. All her classes give her something good, though she should avoid using magic if she can. She could A+ with Azura for Inspiration and Tomebreaker, or A+ with Sakura for Renewal.
Takumi (Offense):
Takumi's strength is average, but the Fujin Yumi pretty much one shots everything so it balances out. The rest of his stats are good to excellent except his def and res. In particular his skill is wondrous. He should A+ Ryoma or Hinata to grab Astra and Life and Death, as well as Basara for Rend Heaven and Quixotic.
Sakura (Offense):
Falcon Knight (Warding Blow) and Kinshi Knight (Air Superiority) are both good. Transition to Priestess then Onmyoji for final class. Hana is the only A+ option that makes sense, granting life and death as well as Astra (Sakura only has ok skill growth however, consider skipping).
Hana (Offense):
Hana has good Strength, Skill and Speed with poor everything else, making her an obvious offensive unit. Grab Swordfaire, Astra, Life and Death from her starting tree. Her secondary doesn’t do much except maybe Renewal. She can A+ with Setsuna, giving her Air Superiority and Amaterasu…or A+ with Felicia and get Tomebreaker and Inspiration. I think the latter is better, given how Hana has bad res.
Subaki (Support):
Blegh. For someone who is hyped up to be perfect Subaki has gross stats. Everything is below average except skill which is barely better than average. Consider skipping training him. Who the hell designed this unit?
Subaki should A+ with Azama. Hinata gives him nothing, and Saizo's replicate is wasted on such a mediocre unit. Lethality is also wasted on Subaki because it needs an insanely high skill growth to activate with any consistency. With Azama at least Subaki can get renewal to patch up his mediocre HP.
Consider making Subaki a support unit. If he marries Felicia/Azura and A+s Azama, he gains access to a total of 4 rally skills. The last slot can be filled by Amaterasu or Inspiration.
Saizo (Offense):
Saizo's kind of similar to Kaze, but with an actual (albeit only ok) magic growth, worse luck and res, but better skill and def. All of his classes are good. Astra works well with his insane 80% skill growth. The only A+ that gives Saizo anything is Subaki; take it.
Ironically for someone with some semi-decent magic, Saizo doesn't have direct access to any magic classes, but can marry one if his magic develops more.
Orochi (Support+Offense):
Orochi has phenomenal mag, good skill and res, but mediocre to terrible everything else. Onmyoji and Tomefaire's frankly probably overkill, but most of her classes have something good to offer. She can consider skipping merchant, though her damage will be great enough without spendthrift and her luck isn't high enough to reliably activate profiteer.
Orochi should A+ Rinkah. Her other A+s have some interesting options but there's wastage from overlap and nothing essential for the remainder. Rinkah gives Orochi Death Blow, which can be devastating, and lancebreaker can be useful too to cover her weapon triangle weakness.
Rinkah (Defense):
Rinkah's one of only a handful of people to reliably get good def, with a respectable 65% growth. She pays for this with her weak offensive potential, and the rest of her stats are average at best, with major weaknesses in HP and resistance.
Rinkah gets good options from both Oni Savage branches. The ninja branch doesn't offer her much...her skill is too low to make practical use of lethality (unless she gets Quixotic?), and her res and HP are too low and make replicate risky.
Rinkah should A+ with Oboro, who gives her some good seal skills, and Rend Heaven to bolster her weak damage.
Kagero (Offense):
Kagero immediately stands out with her mighty strength and speed growth, allowing her to double and double hard. She's held back by her shaky skill and weak luck, with really bad HP and defense. Her resistance is pretty good though.
Kagero benefits GREATLY from Basara's Quixotic due to her poor hit rates. She gets practically nothing from Onmyoji because her magic is terrible. Replicate doubles her already incredible offensive potential. Master Ninja's the obvious end game choice for her with her affinity to shurikens.
Kagero's A+ is debatable...should Rinkah gives her the mighty Death Blow skill and Lancebreaker from Blacksmith, while Setsuna gives her Certain Blow, Air Superiority, and Amaterasu. If Kagero's skill has turned out ok, then go for Rinkah. If not, then Setsuna's skillset covers her weakness nicely.
Oboro (Offense):
On paper Oboro looks about average, but for some reason she always turns out superb for me. She's solid to average in most categories except weaker than average HP and resistance.
Oboro benefits from all her base classes, and should end the game as a Spear Master.
Oboro should A+ with Rinkah or...Mozu? Rinkah gives Death Blow once again, and counter might be good for Oboro as she's often on the front lines. Mozu makes Oboro a flier killer and passive healer.
Hinata (Offense...?):
For a meathead whose support convos revolve around strength, Hinata has surprisingly weak strength. He's got solid HP for a Hoshido unit, and excellent luck. His defense is salvageable too. His speed is really weak however, and his skill isn't great.
Hinata REALLY gets the most out of the blacksmith class with salvage blow. He gets little use out of Astra.
Hinata could consider A+ing with Kaden for Quixotic and Rend Heaven, to boost his offensive capabilities more. Both of his other A+ options are good though: Takumi's particularly useful if Hinata's skill turned out crap, and Subaki's useful for covering Hinata's bad Res growth with Warding Blow.
Hayato (Offense):
This is the best the mighty Wind Clan has to offer? I was hoping for something better than a 55% Mag growth. The fact that he's a clone of Ricken, who I hated, doesn't help. Hayato has good speed and luck growth however. His skill is poor but rescueable with a few good levels. Poor def and res though. His main strength lies in his versatile offensive classes.
Hayato benefits greatly from all his classes. Tomefaire might actually make the difference for him compared to Orochi, and Death Blow expands his offensive potential. Blacksmith is actually quite sweet for him thanks to his high luck growth benefiting Salvage Arms. Basara gives Quixotic and Rend Heaven, both useful skills.
Hayato should A+ Kaden to further expand his offensive potential.
Setsuna:
Most of Setsuna's stats are middling, save her monstrous 75% speed growth. Her poor defenses can be easily forgiven since she should primarily be an archer. Celebrate whenever she gets a strength or luck level.
Setsuna benefits from all her classes save Master Ninja; she'll essentially never activate lethality due to her unremarkable skill growth. She should end on the Sniper class due to its S rank potential in bows.
Setsuna should A+ with Hana, for Astra (higher chance of activating than lethality) and life and death as well as seal strength.
Azama (???):
Azama's basically a psychopath who enjoys torturing other people. Who the hell wrote this unit? Why do so many characters in Fates seem so...off?
Given my great dislike for him it's painful to admit that Azama's a pretty solid unit. He has solid to above average HP, Str, Skl, Spd, and Lck, with salvageable def and res and even his worst stat, magic, is a survivable 30%. With a little luck he can turn into an absolute beast.
Choosing Azama's A+ is difficult. Subaki is better for Azama if he continues being a healer or if he goes full offense thanks to Warding Blow and Darting Blow. The others give him Quixotic and Rend Heaven, which are also good for offense. If his skill (or somehow magic) develops well then go for the latter; if not then go for the former.
For laughs, Azama could consider marrying Rinkah for counter, which stacks with his personal skill.
Kaden:
Kaden's a solid unit, with good HP growth (for a Hoshido unit), ok strength, salvageable skill, good speed and luck, and GREAT resistance (for a Hoshido unit). He can pick up Basara for Quixotic and Rend Heaven before settling on Nine-Tails as his ending class.
He should A+ Hinata; his high res means that Azama's Great Master benefits him little, and his terrible magic means that Onmyoji's largely meaningless on him.
Reina:
Oof. Reina's speed is good and strength is passable, but the rest of the stats? Yikes. Skip.
Yukimura:
Yukimura has serious offense potential thanks to his potent skill lineup. While his stat growths are uniformly bad to terrible outside of his half-good skill, he gets merchant (spendthrift), mechanist (replicate), swordmaster (astra), and master of arms (life and death). His best final class may be swordmaster to take advantage of swordfaire.
Scarlet:
Scarlet would actually have been quite interesting had I made my avatar a samurai for vantage, sorcerer for vengeance, or oni savage for death blow, but I did not.
She's still worth considering for her rally defense alone, from wyvern lord. Scarlet's decently balanced, favoring skill, speed, and strength. Aside from her bad res and non-existent mag the rest of her stats are below average but workable. She's got some good class options though I consider the outlaw line largely useless.