Bell is always the strongest of his level so no level 5 is stronger than him, at least in theory.

But I'm talking about the women around Bell, Tiona, Tione, Riveria, Shakti and Tsubaki are not in Bell's orbit, what reason could Ryuu have to think that Bell's yearning is Riveria or Shakti...?

it could only be a woman stronger than him and that Ryuu perceived to be close to him, obviously she could only be Ais.

Tiona spends almost as much time near Bell as Ais does post Volume 5 MS.

How does Ryuu know for sure who is Bell's acquantance and who is not? Only us readers know. And Ryuu knows Bell made acquantance with all Loki executives in DM 5, the time Loki Familia saving Bell's party in floor 18.

Bell's stronger than his level but a veteran adventurer can still beat him with higher level, technique, and experience. That's why I said maybe.

P/s: Yearning for Riveria is a perfectly valid choice.

Correction, it was in volume 17 when Bell told Ryuu that he longed for someone stronger than him.

In the story "the hero and the prostitute" there is a "fight" where Ryuu, Ais and Tiona face each other to see which of them has been closer to him as a teacher and Ryuu confirms to Ais and Tiona that they were his main teachers but that now she is, ergo she knew perfectly well that Bell had been close to them for a long time.

There is also the SS from volume 16 where the waitresses are spying on Bell and Syr's date and Lunor says that she was expecting a fight when they ran into Ais, which clearly shows that in the hostess of fertility it is known that Ais was the rival of Syr.

Referring back to volume 17, Freya literally tells Ryuu that she will soon free Bell from the "golden curse" and when Ais invades Folkvangr and rescues Ryuu, she is jealous that Ais asks about Bell and refuses to tell her where he is.

So, there is no doubt that for volume 17 Ryuu had already deduced who is Bell's yearning.

@Longhatruong, it's ok to want evidence but not suggesting ridiculous things like Bell's yearning may be Riveria just for the sake of alleging since that has no literary support, much less sense.

Note that until the beginning of volume 17, Ryuu believed that Bell corresponded to Syr and was puzzled when Bell told her that he had rejected her.

I'm gonna have to side with Leinad on this one. Ryu knows it's Ais that Bell likes very definitively by the end of Volume 17 at the latest.

There is also the SS from volume 16 where the waitresses are spying on Bell and Syr's date and Lunor says that she was expecting a fight when they ran into Ais, which clearly shows that in the hostess of fertility it is known that Ais was the rival of Syr.

Or maybe they realized it right at that moment because of Syr action.

Referring back to volume 17, Freya literally tells Ryuu that she will soon free Bell from the "golden curse" and when Ais invades Folkvangr and rescues Ryuu, she is jealous that Ais asks about Bell and refuses to tell her where he is.

Yes, she realized it was Ais at this time already.

So, there is no doubt that for volume 17 Ryuu had already deduced who is Bell's yearning.

I was saying she got the hint from the goddess festival in vol 16 and realized it was Ais when Bell told her he longed for someone in vol 17. What I mean is that Syr's action told her it was Ais instead of deducing from something vague like who is stronger than Bell. There were still plenty of women stronger than Bell at that time.

it's ok to want evidence but not suggesting ridiculous things like Bell's yearning may be Riveria just for the sake of alleging

It's no evidence. It's clearly just a joke so I put it in p/s at the end.

What was the hint in Vol 16?

The only time Bell and Ryuu interacted in Vol 16 was when Freya Familia attacked.

Ryu saw Bell, Syr, and Ais interact. If she was savvy enough, she'd have picked up on how Syr instantly treated Ais like a rival. Though given her state at the time, she may not have.

Ais and Ryuu briefly when she recovered her memories had a small cat fight due to Bell.

I am not joking Ais got territorial during this volume where Hestia used her fire to break the spell.

It was a brief moment the English translation shows this.

Bell should make up his mind and dump all the girls that he is not interested this stupid game that Oomori plays is very stupid.

Bell is not Issei that desires a Harem to live happily about first he doesn’t have the Will and determination to do this.

Harems take a exemplary effort and the boy is clueless when it comes to women.