[Lex79]

My predictions:
Sairaorg Bael vs Shooting Star: while I like Sairaorg he already had his spotlight in volume 10, I think he is going to lose in order to push the new characters.

Indra vs Mahabali: Indra is too hyped to lose against Mahabali who never really had a role in the story.

Issei Hyoudou vs Rias Gremory: the tournament wouldn't make sense without Issei.

Diehauser Belial vs Zeno: same for sairaorg, Diehauser already had his arc, now he's going to lose to the new guys.

Cao Cao vs Surtr: I can see cao cao meeting vali in the semifinals.

Ruval Phenex vs Typhon: dont' really know, probably Ruval because we haven't seen anything about him while Typhoon already had a match in volume 25.

Dulio Gesualdo vs Tobio Ikuse: Tobio is the main character of his own series and has connections to vali, so I think he will win and face him in the next match.

Vali Lucifer vs Sun Wukong: vali isn't going to lose unless it's against Issei or the last boss to be avanged by Issei.