Random fluffy headcanon:
So, Five's powers seem to conserve momentum through a jump--see when Luther throws him off the stairs in S2E5. (Insert Portal "speedy thing goes in, speedy thing comes out.") Also based on this clip, he can change the direction of the portal, since he goes in nearly vertically, and turns it horizontally to not, you know, pancake.
With this in mind, I think Five could do a very fun approximation of skydiving/flying. He'd probably start out by jumping off a roof, let himself fall to very close to the ground, then flip the portal direction 180° and fling himself into the air, repeat until maximum velocity. He could probably slowly build up speed instead of jumping off a roof, but given how his powers seem to run out and who he is as a person, he'd likely find the roof a "more efficient option."
The very fluffy option, besides the mental image of a pre-apocalypse Five flinging himself into the air and giving everyone watching (including the neighbors) a heart attack, is that in a fit of sibling-to-sibling compassion, he'd do this with Viktor.
The way I see it going down is that Viktor would be feeling down about not having powers again, likely after special training or maybe even a mission. Five would see this, and tell him to meet him on the roof after lights out, no they're not all going to Griddy's, it's just for him, since the others already have powers. And it's more fun to imagine that he hasn't shared this ability yet, so Viktor really isn't sure what's going to happen, but he meets Five up there. Hr asks why, and Five says that if he wants, he can give him the power of flight, for a little while at least.
He's surprised, and extremely anxious, because honestly what the hell Five. He's asking Viktor to jump off a roof for fun. There's no way this could go well. But he trusts Five not to murder him on purpose, and when he says he can do something, he can do it. And, really, Viktor wants to know what it would be like, to have powers, to fly. So he accepts, and they jump off the roof.
Falling is the most frightening thing Viktor has ever done, by a large margin, and he's sure as the ground approaches that he's really going to die now. Then there's the swooshy feeling of Five's jumps, and suddenly they're going upwards, and the wind is in his hair, and when he finally manages to open his eyes to peek through his fear, they're high, high above the ground. Then there's a frozen moment when they're suspended in the air, and sure, Five's doing the work and he's grinning at Viktor in that annoying smug I-told-you-so look he gets far too often, but it almost feels like it really is Viktor's power, and he's the one doing it. It's the most thrilling thing he's ever done.
Of course, Five leaves eventually and all that, but once everyone gets reunited, it definitely gets brought up again. Viktor as an adult is appalled that he jumped off the roof as a child. Also, apparently he can really fly, so there's that. He probably wrote about it in his book, so once they eventually remember about it, the other siblings get curious and want to try, so Five goes flying with all of them, and even if he says it's ridiculous, he smiles the whole time.
Luther screams on the way down and denies it, and decides it's not his thing.
Diego very pointedly does not scream, but gets a little dizzy after too many jumps, so only does it a few times in a row, and very infrequently.
Allison screams on the way down and does not deny it. She doesn't like it the first few times but eventually really enjoys it. She doesn't do it very often anyway, because she feels very immature doing it and very seen when they get too high, and that's not a combination she's often in the mood for.
Klaus is ecstatic about this, and shrieks at the top of his lungs. This is his jam. When he wants to go flying he asks Five if they can "get high together." Five is not amused, and also completely misunderstood the first time Klaus asked that way.
Viktor finds it just as fun as the first time, and both nostalgic and freed by being able to do this again. More than the flying, it feels like Five is really back, and it's that more than the adrenaline and illusion of powers now that makes her happy.
When Claire comes to visit, he definitely takes her flying. It's Claire's new favorite thing. It's Allison's new least favorite thing. Allison knows Five wouldn't endanger Claire, but also, she feels she really can't condone her child jumping off a roof, so it's a point of debate whenever it comes up. They still get to do it sometimes, and Claire will occasionally announce afterwards that Five is "the best uncle." Five is smug and gloats for days afterwards, to the point of absolute insufferability.
As for Five, it's been a long time since he's had fun with his powers. When he can finally accept that he doesn't need to save the jumps, the energy, and can just do something that makes him happy, it finally feels like things are okay.
