Nami's ultimate can come in very handy for initiating on enemies who are far away. Using Ebb and Flow during an engagement with enemy champions will help sway the battle in your favor. Aqua Prison has a long cooldown, make sure to use it at the right moment. Use the time after Sion has died to reposition and prepare for his return. Even if Sion still hits a Decimating Smash, making him release the charge earlier reduces its impact. The stats shown on this page underscore some vital Nami versus Sion matchup stats that may help you explain the differences and similarities between the pair.
This observation is in large part fueled by the differences in assists. Nami often has a slightly smaller longest killing spree than her foe does. Commonly, she takes less damage than Sion. This often reflects differing health capacities, but it can also show that the one champ has less mobility and thus is unable to flee from further harm when engaged or poked. Both LoL champions are great. Both have their pros and cons. In League's current meta, Nami usually fairs equally well when playing against Sion, with a Therefore, Nami makes an ok counter to Sion.
While Nami does have a higher win rate than Sion, when on opposite teams, Nami also has a greater difficulty level that makes her a more time consuming character to develop with. You still need to be cautious when picking Nami into Sion. Moreover, Nami has a very large amount of CC and other utility, a similar amount to Sion. This often makes her just as valuable during teamfights, especially when fighting champions with a ton of burst damage. While there is not a single best champion in League of Legends, in Nami vs Sion matchups, Nami is the better champion with a similar win rate, similar champion depth, and a similar amount of utility to help out your allies during team fights.
Nami is a decent counter to Sion. You will do well by focussing your gameplay on keeping up your CS and taking out objectives. If you do that, you should be able to stand on your own as Nami against Sion.
If you mind the build and suggestions displayed here, you should increase your win rate significantly and be that much closer to League of Legends pro players. Nami most often picks up a lot less CS compared to Sion.
