So, I'm rank 105 and I think it's about time I started grinding out tier 4 classes. Problem is I don't know how to go about it and I haven't done co-op at all... any tips/guides?
https://gbf.wiki/Class_Champion_Weapons
That'll tell you what you need to get.
Since you haven't done co-op at all, you need to unlock the EX fights and start farming them. Decide on the weapon and element you want ahead of time so you can focus on farming the mats. The two most common class weapons are Oliver and Nirvana. Oliver because gun weapons pieces are easy to get from the casino gun there and Nirvana for cheesing fights as a sage but also because staff weapon pieces aren't in as high demand as other weapon types. Just start knocking each part down one by one and be sure to hit up the corresponding elemental showdown as the rotate to get the animas from there.
Now, the 'hardest' part of the grind are a few areas but I want to note that the class weapon grind has been eased so much over the last year the things I'll be listing are really not that bad and one of the last tough parts, the weapon stone requirement, is getting reduced for your first class weapon soon. When I say 'hard' it's more just how much time you'll have to invest waiting for drops.
First off,
silver centrums. These can be gotten from gotten from leeching a lot of grand order for feather/horns to turn in once a month for a silver(Time consuming), hosting Grand Order (Comes in the host red chest/easiest way), Rose queen and a few other places. As I noted, hosting GO is the best and easiest way to go about this. I'm not sure if share chests still require a crew member to be in your raid to unlock after the fight but even so, the centrum can also drop in there. Don't confuse silver centrum for the other elemental centrums from HL magna fights, since those will always drop from them. It's by far one of the easiest items to grind. Next are class distinctions, which you can buy for HL renown called prestige. They're 20 per, as long as you do your HL fights and collect full honors from it, you'll finish the element centrum and distinctions in one go but won't worry if you don't, they're so easy nowadays you'll be running them a few millions more times anyway so this will finish by itself. After that, since you don't likely have a stockpile of sky blue crystals, is to so your coop dailies for one a day along with leeching Grand Order fights for them. GO fights can also drop the animas required to host her so you can get a lot done by jumping into as many GO fights as you can for Sky blue, animas and horns/feathers.
Creeds aren't 'hard' to get, they're just a little rare but the EX stage lost in the dark is so easy with a fully buffed room and in an hour you'll likely get 1/4 to 1/2 of the creeds you need. Of course, that all depends on your love for RNGesus and his love back. Continuing on, hit up those showdowns as they come around for their Anima. If you're up to the task, the maniac fights can also drop the items gotten from the Co-op version but don't worry if you can't, the co-op versions are way easier if you have a weaker grid. And last is the ancient cloths. If you've gotten a GW character, you know where to get these. If not, they're from ch 34/71 Antiquarian Troubles and it can be done twice a day. Be sure to hit that place up on 1/2 off.
That's all I can think of at this time and I'm sure the others here will give better input on some of the other aspects I mentioned or didn't.