My prediction has always been that the "Ais arc", which will most likely be shortly before the Dragon fight, will conclude with Bell becoming Level 6, thus him finally achieving his goal of reaching Ais' level. And then the conclusion of the series post-Dragon fight I can imagine a possibility of both Bell and Ais becoming Level 7's together.

But no, I don't think he's going to become the strongest adventurer, Ottar, the Loki executives, etc. will still ultimately have them beat out.

I seriously doubt that the "Ais arc" will be with Bell at level 5, from what we've seen since he reached this level, he still doesn't have enough power to be of real use to her, and he's completely estranged from the Loki family and there's no clear motive for this situation to change anytime soon.

So, I imagine that their adventures together will be when Bell is level 6, okay, they might share moments together with Bell at level 5, but that will at most be meaningful to him, not to her, which is why it wouldn't be a true "Ais arc".

I also don't understand why you suggest that they reach level 7 after the fight with the dragon, what use would that be to them then? It seems more sensible to me that they reach it just before the fight or during it, as a means to play the main roles during the conflict, as would be expected of the protagonists.

The major indicator is that we are very likely in the final third of the story, and the mystery of Ais' backstory is the biggest plot thread remaining, besides the more obviously endgame stuff like what is at the bottom of the Dungeon, or actually defeating the Dragon. Because of that I imagine we're only just a few volumes away from Ais' arc starting in earnest.

Ais' personal character conflict has been that she's always wanted someone to save her, but is now so strong she feels that can never happen, so for the arc to culminate in Bell finally reaching her and becoming close to her equal, feels the most thematically relevant.

And a big theory I and I've seen others share too is that the OEBD possesses some kind of connection to Aria, possibly in a similar way to the assimilation the spider creature used on Artemis in the movie, and that Bell and Ais' main roles in the battle will be to sever it. Thus, could reasonably see them doing that as Level 6's, since I also don't expect the Dragon fight to happen that long after Ais' arc is concluded.

Unless Omori double levels Bell he will be around mid 6 to 7 by the OEBD arc.

If you take Omori at his word there are 2 major arcs post LN20. Bell hasn't been generating much excelia over LN19 so he will start the Ais Arc as a mid lv5 with Asterius probably being his feat for lv6.

OEBD is next and he will probably mid lv6 when they start the serious part of OEBD fight.

The problem is that Ais specializes in killing monsters, so even with his status excess Bell is not even close to match the combat abilities (it would be a different story if she was fighting people but after the faction war, there is no familia left who can pose as threat) Ais have against monsters. This is a big part of why Ais was sidelined as she could have soloed 90% of the threats Bell faced. There is a reason the Ryuu Arc started right after Bell & Ryuu were on the same level.

Addtionnally, we're still waiting for this promissed training session since volume 11 who was reconfirmed in volume 17 which is obviously a special progression card from Omori to take Bell from mid to high in no time. So technically it only require 1 book for Bell to level up which can happen in Volume 22 if Omori decide to adapte the Grand Day Event.

Agree that Ais arc would start when Bell becomes a lv6. Though I genuinely wonder if that training between Bell and Ais is still gonna happen when Bell now has Hedin and other Freya elites to train him.

To me it feels like there's two outcomes: for the scenario when he becomes a Level 6 after the Ais arc, he doesn't confess to her because he knows her past and her feelings about the OEBD, so puts it to the side so he can help her deal with the Dragon first. Or, in the scenario where he becomes a Level 6 before the Ais arc, the impetus becomes him confessing or trying to confess to her, which spirals into him learning her history.