Lea's first thought upon waking was that becoming a Nobody and being essentially split into two was incredibly painful and therefore was a process he hoped never to repeat.
His second thought was that he was desperately craving some sea-salt ice cream.
Time passed. He took a new name and slowly forgot what it was like to have a heart to begin with. He was reunited with Isa, and they joined the Organization. But things were different. Isa—Saïx—was more distant than he had been when he was a human, and their plans had taken a backseat to handling whatever was going on in the Organization at the time. But it wasn't just Saïx that was throwing him off. It was somehow…everything. Nothing felt…right anymore. It was as though everything had been plunged into the darkness of a late evening, where everything was tinted with shadows and starlight.
Axel eventually decided to blame that on his newfound lack of heart, and didn't dwell on it.
And then XIII came, and it was like the sun had finally risen.
He was identical to that boy he'd met so long ago in Radiant Gardens—/Ventus/ Axel's mind helpfully supplied as he examined the newcomer. But Ven's cheerful disposition was nowhere to be found, and this boy went by a different name—Roxas. When he showed no signs of remembering the meeting of their past selves, Axel began wondering what Roxas' connection to Ventus was, if there was a connection at all.
Shortly after Roxas' arrival, they were sitting on top of the clock tower in Twilight Town, talking about hearts. There was a part of Axel that really wanted Roxas to say something to link him back to Ventus.
"Roxas… Are you really sure that you don't have a heart?"
"I dunno. I can't… just look inside. But I figure… if there is something in there—inside us, then we'd feel it wouldn't we?"
"True enough." Axel smiled slightly, handing him an ice cream.
In that moment, he decided it didn't really matter anymore.