I'm not a man of many words.

It's a strong support build that first maxes mana regen, then cooldown reduction and afterwards team aura items. After the first two steps, she can cast a spell every 1.4 seconds without ever going out of mana.

As a side effect this makes this build incredibly easy to play, as even a monkey could punch those buttons. Only see that your team groups around you. As a proof how easy it is to play like this, I am right now writing this guide while playing Infinite Casting Support Sona in a 5k ELO ranked game. It's funny, because it's true.

Your team will love you and the ladies will want your babies (use contraception!).

This build starts with champion selection, where you select Sona and lock in. Then you say hi to each player to gain +Friendly from your new mates. Remember, you will spend some time with them so always be nice. You may want to improve morale by making a good joke. "I def fountain" always get's people laughing hard and laughing get's everyone relaxed. People are saying, that one plays better when one is relaxed (I just said it).

I don't have to tell you that everyone else should pick a good team, it should be known by now.

You, of course go bot with your ADC and keep him happy and safe. As soon as you get well equiped on mana reg, you start punching q, w, e, q, w, e, q, w, e rapidly and without ever stopping. It increases your mana and normally does something reasonable.

Later you win the game.