Watch this video and skip towards the end as they come off stage:

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As Tomi comes down the ramp at 23:13 she is holding a blue bottle.

Then at 23:18 Haruna comes down the ramp and says "Tomo" whilst hiding the blue bottle behind her back... What's going on there?

Perhaps some cheeky Saké?

I'd say product placement, but there's not a clear label on it, it just looks like a generic flask to me.

Maybe it's the secret ingredient that gives them their super powers?  

Thoughts?

***ANSWER: It's Pocari Sweat, the Japanese equivalent of Gatorade/Powerade.***

It's probably just a recognizable brand in Japan that they aren't doing product placement for so Haruna told her to hide it.

Might have something a little extra though :D

Pocari Sweat bottle

It's Pocari Sweat. It's like the Japanese equivalent of Gatorade. They actually did an ad campaign for them before. But yeah, the not so subtle hiding of the bottle most likely has to do with advertising rights and sponsorship.

Haruna senpai keeping an eye out for the flighty Tomo...hehe cute. I like Mami's expression, it's like "Oh geez..."

Haha ah! Thank you guys for clearing that up.

I would've loved it to be a cheeky alcoholic drink of some kind, the videos I've seen of the girls when they're tipsy are hilarious.

POCARI SWEAT! Hahaha!

Haruna really is a leader!