Benimaru:
Shuna:
Hakurou:
I decided to propose the 3 Kijin/Oni right now who can qualify.
What's the Work?
That Time I Got Reincarnated as a Slime is a Light Novel series by Fuze which got originally started as a Web Novel, it eventually became Manga, Anime, and has spin-offs, a mobile game and console game.
Who Are They?
Benimaru
Benimaru is righthand of Rimuru Tempest and general of the Jura-Tempest Federation in charge of military operations and brother of Shuna, son of late Ogre Clan chieftan and husband of Albis and Momiji later on.
Shuna
Shuna is priestess that serve under Rimuru Tempest and younger sister of Benimaru and daughter of the nameless Ogre Chieftain who part of the Jura-Tempest Federation government.
Hakurou
Hakurou is the husband of Kaede and father of Momiji who is sword instructor of Ogre Village and later the Jura-Tempest Federation as one of Rimuru Tempest's subordinates.
What Makes Them Close to Pure Good?
Admirable Standards
Oh boy they would need to compete with Souei, Shion, Diablo, Testarossa and many others of Rimuru Tempest's subordinates who all work under them since they done them together here.
Although three has shared some their heroic actions toegther, they done some enough on their own here since three one of Rimuru Tempest's major key figures besides Souei and Shion here.
Admirable Actions?
Benimaru
He would play major key roles against Orc Lord, Charybdis and Falmuth Invasion leading one of the counterattacks of Tempest’s army into many battles and leading them into victory here.
He would lead Rimuru’s Forces in preventing Clayman’s army from attacking the Beast Kingdom and taking down Charybdis a Generic Doomsday Villain when it was revived by Clayman.
In the Eastern Empire Invasion he would play a major role leading the forces of Tempest into battle and would battle against one of the Eastern Empire generals is in duel and won.
He would stand out from Shuna and Hakarou for being major player in leading Tempest's forces in battle and defense being reason the nation still survives.
Shuna
She played key supporting roles in Orc Lord, Charybdis and Falmuth Invasion attack. Especially during the latter when she helped Mjurian support a barrier to keep souls of victims killed from a earlier attack from dispersing to buy enough time for Rimuru do Demon Lord Awakening to revive victims of Rimuru City wrongfully killed.
Later on she did redeem Adalmann, one of minions of Clayman into a better person who would be heroic character and his own actions.
When Rimuru trying to have his nation enter the Western Nations she would play a role in Rimuru having his nation entering the Western Nations as she did stop a potential attack on her master by simply incapacitating the attacker being Gaiye.
She also has role in caring with injured in major conflicts in Tempest and would cross the G.Z where she was able to undo the mind control of Feldway’s victims thus freeing them from the NPE’s control.
She lacks the army of Benimaru has and isn’t a combatant rather a support so she would stand out from Benimaru and Hakarou despite lacking action she lacks real combat abilities of melee only magic.
Hakurou
He trained several characters such as Gazel Dwargo, Rimuru Tempest, Benimaru, Gobta and etc into formidable fighters who they are making him have impact through his actions that allow them to do their heroic actions. Including a key role of destroying barrier crystal in Falmuth Invasion weakening the people in Tempest.
He like everyone else would play a key role in the Eastern Empire Invasion in defense of Tempest going against one of the Eastern Empire’s generals.
He would stand out since he did train some characters like Gazel Dwargo, Rimuru himself, Youm, Gobta, Benimaru, and more with lacking Ultimate Skills of Benimaru and Shuna.
Possible Preventing Factors?
All Three
Though in earlier stories they were more reliant on Rimuru to act they would become to act more independently and thus don't fail under orders because of it.
Benimaru
He only married Albis and Momiji because marriage was arranged and he did accept it later on despite appearing corrupting on paper. Demi-Humans have different age standards than humans thus isn’t corrupting.
Although he has ability to control his forces it isn't considered corrupting since they sworn loyality under him and help boost efficiency in combat that more benefit than harm must plus isn't painful making too willingly to be corrupting.
Hakurou
Despite how cold and harsh he is, he is a good person at heart and can be friendly to allies.
What Prevents Them from Being Pure Good?
Benimaru
He shown to be wrathful and lethal at times as he tends to get worked whenever Rimuru Tempest is disrespected or seemly think is insulted makes him a bit too wrathful for PG but when compared to a berserker like Shion a IA, he is more calm than her as he less prone to getting angry than her.
He is also lethal at times as while most of his kills are justified or excused, he can be a bit ruthless and remorseless such as killing some knights with some pleasure in Falmuth attack but given the circumstance it isn't too corrupting.
Shuna
She ends up butting heads with Shion at times over Rimuru’s attention, preventing her from being Pure Good. She also has a few mischievous moments and can get envious but is a minor prevention since it is played for comedy.
Hakurou
He shown to be cold and harsh with his training methods as they tend to cause some of sort of injury but given he does his harsh training methods for good intentions plus some like Gobta annoy him into doing them make them rather excusable enough to not be too preventing.
He also shown some lethality at times such through said harsh training methods.
Verdict
A yes to all 3.