"I pulled Hrid +this -that. What do I do?"

First of all, please have a read before you post. There are definitely questions I leave unanswered, but it's good for the Q&A section if the whole page of questions isn't Hrid IV questions. Also, if you have IV questions about other units you pulled from the legendary banner, take a moment to pop their name and "+atk" or "-spd" or etc. into the GamePress search bar to see what you find. Someone may have asked about your exact IV months ago.

About Hrid, then. His weapon is extremely powerful as long as you can activate its effect. I would expect him to function on any IVs, but of course some are better than others. If you get a bad IV, I would recommend using him. If you plan on getting a better IV later, don't inherit anything rare and valuable to him.

Build ideas:
- base kit. If you're using him on a cavalry team, put a cavalry buff in C (probably hone) and maybe atk smoke as the seal.
- sustain build: use sol and maybe vantage. He hits hard enough not to need the extra damage aether provides.
- alternative sustain build: vantage + heavy blade + aether is good too. He doesn't need the extra damage, but if you can OHKO the opponent with the aether, he might heal back to 100%HP or close to restart the process.
- galeforce. His atk is extremely high, and he has a forced double. Plays rather similar to his blue legendary counterpart, also on a horse. You might want to switch out the A-skill for something like sturdy blow or mirror strike or even brazen def/res, but even keeping DC is perfectly fine. If someone else needs the heavy blade seal and you have brazen atk/res seal available, it's an option to put heavy blade in the A-slot.
- Gimmicky stuff: growing wind + quickened pulse or heavy blade + vantage + DC. Designed to take advantage of his extremely high atk. Growing wind will charge in one round of combat, after which, unleash it on some bunched up units and vantage them all to death.
- support build: his B-skill can hit glass cannons like Lon'qu, but it tends not to hit mages (and to a lesser extent, ranged units in general, since a lot of daggers have res in the upper 20s or higher) or sometimes fliers. If you have +res, you can even use, for example, fortress def/res and get some ploys going, or if you don't, a cavalry buff and drive spd seal or something like that can be good. Don't forget that he can also give extra HP and def to his teammates if they have the right blessing in season.

Some other choices of skills and seals:
- distant and close def, especially as seals
- threatens are actually decent on him because they will enable his prf effect, and he's tanky enough to let opponents into range, maybe even hit him before they activate. Smokes probably are still stronger due to him being quite mobile and cavalry often liking to stay out of the way until they get aggressive.
- guard or steady stance 4 are insurance policies in case he finds himself against a healthy opponent

IV preferences:
For sustain builds, +res is probably preferred, or +def. He already hits plenty hard.
For galeforce builds, +res and +def are still good but +atk might be more reliable. The thing about galeforce builds is that too much atk will sometimes result in some OHKOs which prevents galeforce, but with def getting as high as it can get these days, having +atk can hardly be a bad thing. Just don't use death blow, and keep him away from the hone cavalry if you need to.
For all builds listed above, -spd is preferred because it's so low that investing in it is inefficient, and his HP is actually kind of thin so despite good def and decent res, he can have difficulty tanking multiple hits, and dropping HP would make it tougher.

+HP: is slightly nice for that reason, though not as good as +def or +res because he has good potential to tank multiple hits.
+spd: is actually interesting, especially with hone cavalry. 26 spd is territory where you might double wary fighters, especially if you debuff their spd, which is something you might want to do anyways. This IV has good potential to give Surtr a really bad day because Hrid's 52 atk (after getting debuffed) counts as 62 vs green and he's tanky enough when buffed to take the 20 chip damage followed by a hit from Surtr before hitting twice and sticking a big moonbow in the tyrant's face.

-atk: yeah whatever. Still 53 atk unbuffed; he can receive hone cavalry; he wants his opponent to be debuffed in def. If you combine def ploy with hone cavalry he has virtually 64 atk, which is more than L.Eirika with +atk and atk/spd solo.
-def: unpleasant but doable. In my opinion, easier to swallow than -res because his def is quite high to begin with and it's not a superbane.
-res: is probably the hardest one to swallow. 26 res is kind of marginal for taking multiple hits, but with investment it becomes good. 22 res can still become very decent, but it sets him back a step. With fortify cavalry he's only at 28, and stacking atk smoke gets it to a virtual 35, which is not too bad. I think it's an option to give up on his res and just let it sit at 22.