There's been quite a few cases where someone wants to give another gems, but can't do it because most people assume that they'd have to have access to the person's facebook account to do so, or that they're in the wrong country so they can't give the other Google Play Gift cards, etc

You can use https://www.bravefrontierglobal.com/molasia/index.php to buy gems for other players on Android, simply using their Friend ID (For example mine is 7082787517, won't work because I'm on iOS currently) and I've used this method to give others gems quite a few times. Sometimes there's also promotions where using molpoints to buy gems also gives Altons, Burst emperors or even Rare units (How I got my 30 4* Luka Codes)

Hope this helped at least one person who is now Able to buy gems for their Friend. Have a nice day