In Return of a Friend, he and Mira had an argument because Mira wanted to postpone destroying the dimension controllers and find her brother, however, Ace refuses to allow her to go because he fears of the dangers she may face. In Voices in the Night, he says, "This is for Mira", which may also hint that he likes Mira. After Mira and Baron went to Earth with Dan, he worries about Mira and when he hears her voice in the night, which was really Shadow Prove who was leading him into a Vexos trap, he tries to save her, which further proves his love for Mira.
In What's the Plan?, when he and Shun are forced to fight together in a tournament, Ace wears a purple and black mask to disguise himself while tensions rise between the two of them and they fall close to losing. However, on the edge of defeat, they put their differences aside and Ace works together with Shun after realizing he was just trying to help. Shun remarks that he is very much like Dan. In Voices in the Night, after falling for the Vexos trap laid out by Mylene, he loses in battle to her and becomes a hostage. After Marucho and Shun are also captured, they are relocated to Beta City, where they are freed by Mira and Spectra, though they are unaware of this. When he's told that Mira betrayed the Resistance he refused to believe it due to his feelings for her and gets a little violent by grabbing Dan's collar, but accepts it as the truth when Baron insists Dan's telling the truth. In Wall To Wall Brawl, When the Resistance infiltrate Gamma City, he and Dan battle Mira and Gus. Mira ends up betraying Gus and Ace tells her he always believed in her, Mira smiles affectionnatly at him it may mean that she likes him, too.
After Skyress, Hydranoid, Gorem, Tigrerra and Preyas are rescued, Ace and Percival return to Vestal with Baron and Mira and spread the truth about the Bakugan and the Vexos' actions. After Percival receives the Darkus attribute energy from Exedra, Percival evolves to Midnight Percival. While Baron searches for an apartment to move into, Ace helps out but is ambushed by Mylene. He nearly loses but is saved by Klaus. Ace travels to Earth with the Resistance to hide out from the Vexos and protect the Attribute energies. While in hiding, Julie develops a crush on him after watching him work out. When Marucho invents Bakugan Interspace, Ace is set to battle Billy, but also challenges Julie so as to not "get in between the two love birds." Despite Percival becoming immobile, Ace is victorious thanks to his evolved trap Darkus Flash Falcon Fy. After the Resistance decided to go on the attack, Ace and Marucho encounter Lync and Shadow at the Mother Palace. Due to the rigged field, Ace and Marucho lose and the Darkus energy is taken.
After destroying the BT System, Ace returns to Earth with the Resistance and witnesses Dan's ultimate battle with Spectra, in which he decides to turn over a new leaf. After Keith becomes an official member of the Resistance, Ace becomes jealous of the time Keith spends with Mira. But Julie and Percival assure him that Keith and Mira are only siblings and that Mira is just happy to have her brother back.