Servants I shd focused on to clear Story mode on JP server?

Orion for bosses in Camelot. Summer Medb in Babylonia, though preferably AoE servants. Tamamo and CasGil to support your arts servants. Also Yan Qing and Summer Ushi paired with Skadi for Babylonia.

Though most of the time you could be fine with Summer Jalter since she is a berserker. You could pick Waver or Merlin for supports since Skadi lacks heals and defensive buffs. Her evade in NP is somewhat very situational.

Disclaimer: I'm n NA player so I have no direct experience with JP servants except for reading their lore and usage.

So since you started so late into the game and rolled 9 SSR servants QP is gonna be a pain to manage. You said fast track the story into Lostbelt right?

This is the level priority
1. Gilgamesh (DO the interludes first. Overall an amazing servant whose only weakness is that he was released early in the game and his skills are very outdated but his high hitcounts and NP carry him in the tierlist. So basically even with outdated skills you need to level them up for Gil to reach his full potential)
2. Skadi (Is basically a quick merlin or tamamo however you put it. Max her 3rd skill for the charge in order to blaze away in the mobs or even max her 1st skill if you have a good quick servant and max 2nd as it's a utility skill only for 1 wave. Problem is her mats it's available in Lostbelt 2)
3. Summer Jeanne (AMAZING FARMER IF PAIRED WITH TAMAMO YOU CAN CRUISE THROUGH MOST BATTLES WITH HER. Only problem is the newer mats and you have to get a starting NP CE but those are given out frequently or just use the 3 star leyline CE from the FP gacha the one that gives 50% NP gauge when MLB)
4. Abigail (She is by no means a good servant basically having no np gain at all unless you Arts chain or get outside help via waver, merlin, tamamo and skadi and her trash skills because all of them are on a 9 turn cooldown and aren't worth the effects except for her first skill but her NP is the MOST OP ST BUSTER NP in the game basically a ST Amakusa NP. And again she's high because of her NP and btw she is hard to ascend if you don't have mats then skip her)
5.Ereshkigal ( TBH SHE SHOULD BE PLACED IN THE 9TH SPOT DUE TO HOW HARD IT IS TO GRIND FOR HER MATS DO NOT RECOMMEND UNLESS YOU HAVE THE MATS FOCUS LAST BUT IF YOU HAVE THE MATS THEN GO FOR IT)
6. Summer BB (A unique but meh servant this is due to her low damage but is strong overall due to her 3rd skill because her 2nd skill is realistically only going to be use 1-2 times per fight due to it's cd and having 4 star attack stat and no class advantage to most enemies really hurt her. Still a decent to good servant overall)
7. Tamamo (Just max her Fox Wedding and you can skip her other skills again do the interludes)
8. Orion (Only use her against tough male enemies )
9. Mebd (Orion outperforms her only bring her in Caster fights she does amazing in caster fights)

As for SR Servants / 4 stars
1. Summer Meb (SUPER STRONG 4 STAR SABER the only problem are the newer mats but they are not in high quantities. She can rival most 5 star sabers and pair her with Tamamo )
2. Caster Gil (Amazing caster. Mats however... goodluck farming them)
3. Qin Liangyu (Her only use is in harder fights or gimmick fights and you should pair her with tamamo. But due to newer mats you can take her skills at most to level 7 which is not to bad)
4. Summer Ibaraki (Amazing servant overall who's only downside are some demerits but can be ignored with the right supports. BUT! her mats are disgusting as sht! UNBELIEVABLY BAD MATS 180 gunpowder to max her skills in total and thats locked till Lostbelt 1 though they are easy to farm the quantity is annoying just like Anastasia's gunpowder requirements )
5. You can go for anyone at this point because anyone other than the 4 SR servants I mention you got are pretty meh and not that good.