General

When playing damage rei, you are supposedly playing as a flank just with a lot less mobility, kind of like moji in a way except you can still fight at long range and not suffer deeply. When engaging combat not using your envelop ability straight away is crucial as you may need it later on, to increase survivability and/or too escape.

I've found that it's most benificial to try and sneak up behind the enemy teams backline to be the most benificial. When doing this try not to use your spirit link right away as it slows the enemy, making them know they are under attack right away. Instead, trying to get atleast one or two shots in and then spirit linking to the enemy is much better as they might think they're just taking 'a bit of damage'. It's also because if it's a mobile character (for example evie or maeve) your spirit link can kill them when they are about to escape you. In short, it's basically a "you're too late lol" tool.

I personally aim to kill the damages which lets your team be able to breath due to the lack of pressure on the point. Another reason on why I aim to kill the damages is because you can leave the enemy healers for your flank or off tank to deal with but if they aren't then obviously switch your priority to the enemy support if possible.

Trying to take out the enemy team one by one is a good tactic for damage rei as she shines the most when fighting against 1 or 2 people and not a whole team, this is mostly because of the amazing amount of damage reduction she gets and because she doesn't have any AoE damage (hitting multiple targets at the same time). It's also because her ultimate is an "i win" button when trying to solo kill someone because you get your entire health back up. Most champions, if not all of them, won't be able to anything and will likely end up dead in consequence of underestimating a damage support. Rei solos, literally and figuratively.

Talents

From my experience focus is the better damage talent but restraint is decent, but you rarely get to activate the talents usage anyway due to the high cooldown of envelop. I use envelop as a way to push enemies or as an escape depending on the situation, so if i played restraint it wouldn't be very valuable for me.

Items to buy and why

1) I like buying nimble first because rei just lacks a lot of mobility, her movement ability is only a jump and speed boost, i think it adds DR (damage reduction) aswell but i won't say for sure, just incase i'm wrong. Buying nimble allows you to get in and out of a fight with less risk involved. Just don't run in too recklessly.

2) After you've bought nimble the next item is situational, for example wrecker or resilience would be good in certain situations but if you don't need any items like that, then i suggest getting haven. The tankier you are the better remember. ;)

3) The third item too buy is usually veteran. However if the enemy team has a champion using a talent that damages based on max hp (for example betty's firey disposition or vora's unyielding pressure) then DO NOT BUY VETERAN. kill to heal or morale boost are better options in this situation!

if you've found that your just trading when getting kills (that means everytime you get a kill you die) then maybe kill to heal would be a better option, if that still doesn't work and your still trading, try playing a bit safer and remember to cycle around your abilities better. Or ask a teammate to help you with flanking if you do this, you should be aimming to have the flank or the off tank attack alongside you don't drag the main healer into it, they have better things to do rather then helping you flank the enemy team!!

4) If you haven't already then kill to heal should be your last option. Personally i've never really tested out morale boost dmg rei as the last option but i'm assuming it'll be late game when your picking your last option so you won't get many options to get your ultimate back up as often. So i'd recommend staying away from it unless you have no other choice and are in desperate need to get your ultimate.

Items and Cards i'd recommend staying away from and why

Items

Illuminate

If you spirit link to an enemy that goes invisible, like strix or skye, you can still see them meaning that illuminate is an overkill. As long as your listening to those audio queues that means they've gone invisible or if you can hear their footsteps. Just genuinley start spamming your spirit link and you should be able to find them.

Life Rip

Lifesteal gets hard countered in late game you won't be getting all that much. In every circumstance possible kill to heal will always be the superior option unless lifesteal gets a buff that is uneffected by anti-healing or something along those lines.

Bulldozer

Unless luna or inara's wall is being that much of an issue just don't bother with this item, even though it looks good you're rarely going to be shooting at those anyway thats the damages job not yours.

Deft Hands

Why bother honestly, it's not like the reload time is 25 years long, it's never been a problem for rei.

Cards

Arcane Focus

It only works when your linked to an ally, the only time i'm ever linked to an ally is when they are my main healer and they're about to die. and plus even as a filler card it's 20 health per second, if you do the maths thats 2 heals per second in late game, their is zero point in running this card, even as a main healer just stop pls.

Desperate Defense

I used to use this card all the time in my loadouts but then i realised that when paired with anti-heal it's just not worth it and your better of using something like future generations as a filler card.

Leipori Prayer

Everytime i see this card being used by a rei it just hurts my soul in so many different ways. Even in a heal loadout or not it still is a horrible card to use purely because reload speed isn't a problem for 99% of the characters in the game right now. Stay as far away from this card as possible, it's genuinley one of the worst ones she has. Don't fall into the trap of thinking you'll get stuck in the reload animation when in a fight, as long as your reloading before every fight you take you should be fine otherwise.