If you use your on an ally, E Tidecaller's Blessing it WILL proc the following items/runes:

: Summon Aery
: Font of Life
: Imperial Mandate
: Moonstone Renewer
: Chemtech Putrifier
: Morellonomicon
: Cosmic Drive

So for example, building Imperial Mandate together with an item like Chemtech Putrifier will make your E Tidecaller's Blessing an insane buff for your ally.

She fits into every team comp. And you always have a shot on winning. If that's not important to you, keep in mind she's fun to play and decent blind pick. Her movementspeed makes it comfortable to roam, her heal makes it easy to sustain.

Pros:

[+] High mobility
[+] Engage
[+] Disengage
[+] Heals
[+] No real counter
[+] Fits every teamcomp and botlane
[+] Can shutdown carry champions


Nami has a lot of mobility thanks to her passive, you can apply it on allies and yourself. This also helps with engaging and disengaging as does you crowd control abilities.
Nami has a bit of everything, and great sustain (exept for her mana pool which is fixable) which means she fits every teamcomp and is hard to counter. Her Q Aqua Prison and R Tidal Wave can be great to shut down carry champions when needed.

Cons:

[-] Needs one frontliner to really work
[-] Squishy
[-] Hard to hit Q


Nami really needs a frontliner to work, else she can't setup fights or keep her allies alive. It's possible to make it work, but when your team doesn't have a frontliner, your team is waiting to get caught and die.
Nami is very squishy, which is why I lately go Guardian and Relic Shield this is not a magical solution but it does make you die less. You have to really learn how to position if you do not want to feed. The only other bad thing she has is her hard to hit skillshot Q Aqua Prison. You can set up a slow to land this ability, but in a stressful situation it's unreliable.

A support item is a must-have as support, else you will lose a lot of gold income and vision control. Because lately Relic Shield is a viable option you have to choose. I recommend Spellthief's Edge for the casual players.

Shard of the true ice

You buy it as Spellthief's Edge and it upgrades into Frostfang
into Shard of True Ice as you get gold. You don't have to buy the
upgrades anymore but make sure to trade when you have stacks to upgrade
it sooner. It's the most easy to poke turrets a little when you get the
chance. When this item upgrades you are able to place up to 3
wards with this item, use them for objective control!

Bulwark of the Mountain

After a lot of test games this item is legit a good choice to be safe
in lane. Consider this item vs hook matchups or matchups you prefer
not trading against. This not only denies the enemy laner
gold, but also keeps you healthyer to sustain.
You can save your mana for heals and ganks. Make sure you try to
use all it's charges on canon minions and melee minions for gold.
When this item upgrades you are able to place up to 3 wards
with this item, use them for objective control!

Boots:

Always take boots early against engage support to dodge and reposition faster.

Boots of speed

Movement speed is important for dodging abilities, getting out of a
fight and warding. Though if you are able to survive without them,
you could use that gold to finish another item faster.

Boots of speed Movement speed is important for dodging abilities, getting out of a fight and warding. Though if you are able to survive without them, you could use that gold to finish another item faster.

Boots of mobility These boots are always a good choice because you can roam well, position better, and get your wards down quicker. The boots also give quite some pressure. People tend to rush these when botlane is miserable because you can roam better.

Ionian boots of lucidity Getting this does make you a little more vulnerable, and slower overall. Just test it out.

Boots of swiftness It's now cheaper than Mobility Boots and has a consistent speed buff. This makes it easier to get out of fights and reposition.

Mercury's treads These boots are a great option when you're playing against a team with a lot of cc. It's best to position a way you won't get hit but there are some champions that are hard to avoid like Leona and Nautilus.

Plated steelcaps When the enemy is full ad take this but i don't like this boot like others.

If you're going the Guardian build you probably want to reconsider Ardent Censer. But in any other build these items give you the most power.

Staff of the flowing water This item gives you and your ally a movement speed and damage bonus! If you use the rune Summon Aery you can also proc this item's passive by using E Tidecaller's Blessing. Font of Life also triggers this item just as it triggers Ardent Censer. I think this item fits great playing with Ezreal and Jhin.

Ardent censer This item has more power than redemption. You can proc this with your W Ebb and Flow, Redemption, Guardian and possibly with Font of Life. So when you want to go for something else, go for Redemption and Shurelya's Battlesong

Moonstone renewer This item gives Nami a lot of healing, it sadly doesn't give the mana regen like Athene's Unholy Grail did. The ability haste and the heals are still great.

Imperial mandate this item is the best when your team is snowballing, especially when your team is good lategame as well. Casting E Tidecaller's Blessing on an ally also makes them trigger imperial mandate, this is really strong

Shurelya's reverie In team with good engage this item will be ultra useful. usually get this item for a better engage or disengage

Locket of the iron solari If your team is not snowballing or good at the late game or needs a little more defence against burst. But it's not worth to take it with nami though. The active procs Ardent Censer for your team

You should always consider what your team needs, the enemy has, or what you need.

Chemtech putrifier This item is the ideal antiheal item for a support. but for nami it's better if you use E Tidecaller's Blessing on an ally, it will apply 40% healing reduction on the enemy that ally hits. if you hit a bubble or R as well, the healing reduction goes to 60%. Chemtech Putrifier better than Morellonomicon because mana regen that nami needs.

Redemption This item gives a big aoe heal that is really strong in teamfights when placed well. Combined with other healing buffs like Staff of Flowing Water and Ardent Censer it can give a huge comeback to fights.

Cosmic drive This item is so good on nami give you so much ability haste and mobility. And you can procs it with E Tidecaller's Blessing.

Zhonya's Hourglass This item is great for survive burst, it's great for nami because she is very squishy. It's good against zed,...etc.

Mikael's Blessing It's great to get a Mikael's Blessing this item also empowers your heals by 20%. It's great against chain cc team, you need this item for some magic resist too.

Zeke's Convergence It scales with health and ability power. if you're not thinking about taking Locket of the Iron Solari. Zeke's Convergence also gives 20 Ability haste, which can be useful.

Rabadon's Deathcap build this item, have a lots of ability power. Try it, enemy team will be scared from your damage, and your heals will be strong.