A/N: Since finishing the first part I had several requests for a sequel/extension, most recently from DanverSisters. So here is a brief extension where the roles are reversed. Like with the first 4 chapters this is just meant as a bit of fun. It is set about a year after the original so Alex is dating Maggie and Kara has recently started dating Mon-El (so sometime in season 2)
-A year later...
"What's going on?" J'onn asked as Kara entered the DEO with a small child in her arms.
"We have a problem." Kara said. "One we need Alex to fix, but she can't because..." She then used one hand to point to the child.
"What are you talking about?" J'onn asked.
"This is Alex, at least I think it is Alex. And she says she's Alex."
"Me Alex, you Kara." The child said from Kara's arms.
"See." Kara said.
"I'm not sure." Winn said. "I mean she seems kind of docile and not threatening." He said approaching the pair. As the child saw him though she glared at him and held up her hand, waving her little finger. "Um...I take back what I said. She's still scary." He added backing away.
"How?" J'onn asked Kara.
"I don't know." Kara said. "When I went to Alex's apartment I found her sitting in oversized black fatigues. And there was no sign of adult Alex."
"Let's get her to the infirmary." J'onn said before asking."Is Maggie effected?"
"No she is her normal adult self, I think." Kara said.
"You think?" J'onn asked.
"I phoned her saying I was looking for Alex and she sounded all grown up."
"You didn't mention what had happened?"
"No, I wanted to make sure we were sure first."
-00-
"She's definitely Alex Danvers." Hamilton said glancing over at the toddler who was busy examining some of the medical equipment. "Bright side is this time the anti aged doesn't have powers so she should be easier to control. Down side is she doesn't have powers so could get hurt. So she definitely shouldn't be playing with that." Hamilton said taking a probe of Alex who started to cry. In response Kara picked her up and the crying stopped.
"Any idea how to fix this?" J'onn asked.
"Not until we know for sure what the cause is. I'm assuming that it is similar to what happened to Kara last year. But it is just a theory until the tests come back." Hamilton said.
"In the mean time I'll quarantine her apartment. If there is radiation source that can do this to humans, we don't want the whole city effected." J'onn said before pausing as he thought. Finally he added."If the cause is in the apartment, the only thing we know is Kara's not effected."
"I can't leave Alex." Kara said sensing where J'onn was going.
"I know. But if you're not affected, chances are neither is Mon-El. He can help in the clear up operation...although if it did de-age Mon-El that could be a problem. He is difficult enough as it."
He then looked at Kara and said.
"I assume you can keep her out of trouble?"
"Alex wouldn't cause trouble, would you?" She said looking at the baby who was stretching for one of the medical instruments.
"Hey." Mon-El said entering the room. Noticing Kara holding a the child he added. "You have a baby."
"Your powers of observation are amazing." J'onn said dryly.
"Where? Whose? Is it yours?" He asked Kara.
"No she's not mine. Just my responsibility." Kara said. "This is Alex."
"Alex as in your scary Earth sister? What happened?"
"Possibly a variant on a Gelf experiment." J'onn said. "It causes a reversal in the ageing process."
"I remember my mother talking about a Gelf scientist who was trying to extend life." Mon-El said.
"He was a prisoner on Fort Rozz. We think someone is using his work, only this time it's been modified for humans."
"This time?" Mon-El asked.
"Last year it was used on Kara." J'onn explained.
"Wait, that happened to you? When?" Mon-El asked looking at Kara.
"Last year." Kara said. "We don't talk about it."
"If this does have the same cause I'm guessing the radioactive crystal has a different signature which is why Alex was affected and Kara wasn't. So I need you to come with me so we can secure Alex's apartment."
"Sure." Mon-El said looking again at Alex.
"I'll be back soon." J'onn said to Kara before warning. "Remember she's not invincible."
-00-
"How's it going?" Winn asked entering the room where Alex and Kara were.
"How do people do this without powers?"
"Do what?"
"Look after a kid. I turn my back for a second and she is playing with things she shouldn't or trying to escape or jumping off things." She said before using her superspeed to move over to Alex and catch her as she jumped from a chair."I mean how does she even climb up there. Maybe she has developed powers as well as anti-aged."
"Maybe she's getting revenge. You were kind of a menace when it happened to you." Winn pointed out as Alex started to struggle. Putting her down Kara watched Alex toddle off only for her to trip. Before Kara could reach her she had hit the floor and was crying.
"It's okay." Kara soothed as she picked the crying baby up only this time Alex didn't stop crying.
"Kara." Winn called over the noise. "I'm no expert, but you may be hugging a little tightly."
"Oh, Alex. I'm so sorry." Kara said as guilt washed over her before she handed the baby to an unsuspecting Winn. "What was I thinking? What if I broke something?"
In response Alex, still crying, held her arms out towards Kara.
"Looks like she wants you." Winn said thrusting Alex back into Kara's arms.
"What if I hurt her?" Kara asked as Alex stopped crying.
"You'll be fine." Winn said as J'onn entered the room.
"Any news?" Kara asked.
"We found a radioactive crystal. It is in containment at the moment and we are remotely running tests. If it is a variant of what happened to you we should be able to reverse it relatively quickly."
"Sir, we have a problem." Vasquez said before seeing Alex and saying. "A bigger problem."
"What?"
"There was an attack at the Metro Centre by what was described as a rock alien."
"A what?"
"An eight foot rock like creature." Vasquez said. "It's gone now, but we don't know where and chances are it will be back."
"Sounds like Supergirl will be needed so we need some extra help for Alex." J'onn said.
"You want me to call Maggie?" Winn asked.
"No." Kara said. "Trust me it will make it really awkward for them. Seeing Maggie isn't exactly kid friendly I think we shouldn't tell her unless we can't fix it quickly."
"Agreed." J'onn said. "Fortunately we have access to the ideal help."
-TBC...
A/N: Thanks for reading and reviewing.