I've been really excited for Rintengi's release ever since the tengi batch was announced. It's definitely my favorite sphere in this game, and it doesn't help that the unit has a really unique and cool looking design. Though looking at it, my heart just sank. I expected maybe a better Eriana or something to match the sphere he's based on, but they managed to disappoint me in every single meaningful way. Let me explain why:

First off here's his info so you can have a reference

His LS is absolute garbage.

A LS without any mitigation or BB support is pretty much 100% unviable for hard content nowadays. It doesn't provide anything remotely useful except Null Ailments, but Alza already provides that and it's a common buff to bring to everything. They could've least put conditional miti on his LS, but we're just left with this mess.

The ES is good, but it only exists to keep a unit with extremely common buffs alive.

The AI passives are amazing, but not so much given the context of the unit. 80% chance AI is really good so you can't go wrong with that. Same with 40% stats. The 30% AI is just a nice bonus if you get lucky, it's not high enough like it's sphere counterpart to be a reliable mechanic. This is supposed to play into his UBB where you proc your AI and revive everyone using your own UBB, but I'll get to why that's really meh later.

The BB is just ok. Just ok and nothing more.

Rintengi's gimmick is to be able to "heal more than usual", but it just ends up being big numbers that don't actually contribute to anything. The big heal is so useless when everyone's heals already bring you up to max, it's just there for show more than anything else. Null status ailments and debuffs is alright, and the increased HoT and HP on Hit is the only good part of his BB. Null ailments is on so many units now (and null status ailments is on the most popular LS in the game) that I don't consider it a standout buff. Null debuffs is lol tier. The increased HoT and HP on Hit are good, but are you really going to waste a unit slot taking a walking HoT bot when alternatives with more buffs are easy accessible? Overall the BB is just really bare bones in terms of usefulness.

Have fun getting his SBB to have a low payoff

Again, the heal is a bad gimmick so I'm not going to cover that again. The HP barrier isn't worth it in the slightest, especially given the cost of the SBB. 50 BC fill is just Tilith tier, but it's so hard to get around to getting SBB in the first place (unless you fujin or swap in) that if Rintegi (a unit with only 1 BB support self skill) can get SBB then most of your units should be able to. If you do try to use his SBB, you'll be punished for not using his HoT to buff the squad which is exclusive to his BB. 10% chance AI is garbage so I won't cover that. Boost max HP is alright. Why is status cure on SBB if you can't spam this? Shouldn't it be the other way around where null is on SBB and cure is on BB? Really contradictory design if you ask me.

UBB Revive is so situational that you'll never use it

You can ignore the other parts of his UBB (except the chance AI) since revived units don't get buffed from the UBB. In order to pull off a revive:

1) You have to fail surviving the nuke in the first place or have a unit get picked

2) Rintengi has to survive through natural tankiness or inherent AI

3) Have OD available meaning you either didn't use it to prevent the nuke in the first place or just didn't use it at all

4) Have a fujin ready to dispose of

5) Have a unit ready to heal, mitigate, and apply defensive buffs to the units who don't spawn with conditional miti or defensive buffs.

6) Pray that the 70% chance revive procs on who you want it to.

It's not bad, but the skill is so situational in the first place that there's really no point where you should realistically base your strategy around reviving. This holds especially true in content with a UBB counter. You could take the SP option that gives 90% chance AI on UBB, but then you'd invalidate the main part of his UBB. It feels like less of an upgrade to his SP and more of a superior sidegrade - killing his previous function.

I'm just gonna go over the SP options real fast now since a category on all of them would be too long.

80% HP/DEF/REC

Amazing. Can't go wrong with that.

2-4 BC Fill when Attacked

You need BB support in this era so this is definitely a 100% take if you can.

30% chance of 40% HP recovery when attacked

I mean if the tankiness from stats wasn't enough, I guess this serves to beef up your unit even more. Having a super tanky unit with a subpar skillset really helps.

25% chance to take 1 dmg

Same as above.

Add 20 bc fill for self to BB/SBB

S I X T Y (6 0) SBB COST

Enhances sbb max hp boost by 5%

really?

Adds 4000 Hp earth element barrier to BB

decent, can start spamming an ability that is already used on a lot of common units now.

Adds 180% rec buff for 3 turns to BB/SBB

Where's the rest of the buffs though? All three stats go in pairs now, it's very hard to find a unit with just ATK/DEF buffs to compliment this.

Adds 80% rec to atk for 3 turns to BB/SBB

Inferior convert compared to converting from DEF. Doesn't help that most units are Anima anyways. It could be nice to use, but know there's better options out there.

Adds 90% chance angel idol (Recovers 100% HP) to UBB

Probably the best option he has, but I've already talked about it above.

Overall, Rintengi is just a very lackluster unit. A low amount of decent buffs, an SBB that you'll realistically never use more than once before being swapped out, conflicting skill set, and a useless gimmick that either doesn't matter or isn't worth using over other units with more that they can do. It doesn't help that the unit is super bulky and comes with inherent AI, but doesn't attack meaning he's unviable in colo. I don't know if this is Rayla bad, but definitely in the bottom 20% tier of units. So much for a "strongest units" batch.