User blog comment:SpookyBoogie27/Light Novel Spoilers/@comment-8.28.150.75-20140210041712/@comment-1359322-20140210042856

Issei current goal is Euclid. Issei would probably try to master the Boosted Gear to the fullest to show Euclid the strength of the REAL Red Dragon Emperor, cause Euclid kinda actually really insulted both Issei and Ddraig when he revealed himself as another Red Dragon Emperor which is actually a fake one too. And what's worse is Euclid was able to overwhelm Issei in his Crimson Armor. So i think Issei wouldn't just take it quietly after that huge slap to the face.

As to Rizevim, who knows? But i'm guessing that Rizevim will eventually fight either Sirzechs or Vali maybe both, considering how Ishibumi hyped Vali and Rizevim's relationship, as well as Sirzechs' team being formed to counter Rizevim.