The last reveal about Tanaka (Seiji) being an Android was too much Terminator-like... Being reprogrammed to be the bodyguard of the guy he was designed to kill... Take it with a grain of salt though... His visual identity remembers me a lot of Sir NightEye down to the very calm demeanor using office appliances as weapons (Samurai Flamenco?)... Not sure who came first though... The yandere mode isn't my thing but I give that it's very great visually...
Tokioka (Nagato) has these Sawada Tsunayoshi (from Reborn fame) vibes... Change the President thing for the Greatest Mafia Boss and the Foresight for the Hyper Intuition (add a little of Sharingan for good measure) and it should be set... The party animal thing would be his most original trait. Don't let me forget the Jackie Chan's Tuxedo!
I like mandatory pretty girl Gennai (Tsuruuchi Akari) a lot... Ponytails are a must, and her Trigger face (just the triangle grin) complements the girl gadgeter very well... In a ranking where Lala Deviluke and Winry Rockbell are tied for a 10 she's easily an 8... Her demon face is a little familiar too... Ymmv about how much curvy she still needs to be...
The Vortex managers are all textbook shounen villains? None of them really hit a chord... and up to here we had a full of references very healthy jump manga...
And for the weakest link my vote goes to Saikawa (Kyouhei)... He's pratically Tsukasa Shishio in a sweater vest(1)... Maybe it's the Child Zero from Teenager monster vibe... Or the absurd mix of brain and brawn? Dr. Stone sells Tsukasa as this presence of a gentle caveman that took a lion with an OHKO and at the same timehad the smarts to follow Senku supposed incredible train of thought with ease... Saikawa mimics this by sitting on a pile of "strongest guys" and making the perfect pitch of the situation before the protagonists utter a single word... It's kinda justified that the Vortex Staff aren't the best at keeping secrets, but I still didn't bought how much info he gathered while multitasking a massacre...
Some disconnect nitpicks I still have on him...
I'm sure the IV as a weapon isn't a original weapon choice either, but maybe he deserves a discount cause it's his main weapon?
He intruded Gennai's fight in a very Hibari Kyouya way too... he even has his hatred of everything weak(2)... I'm reaching already... the last second save is a shounen staple...
His main sin is that he overlaps with Tanaka(3)... I DARE to say that Tanaka was made into an android to accommodate him as the strongest human what in its turn harms Akarin's characterization since Tanaka is a super piece of technology capable of complex emotions from just 20 years in the future that her genius self didn't create... I guess that you can say that vortex stole the Cat's AI at some point... but the damage is already done.
My last pick is he drinking poison as part of his Strongest training image... Nietzsche's "What don't kills me makes me stronger" exists, and Goku is to blame of the same thing way back in Dragon Ball... But in this highchool setting using a commonplace poison... Some "virtuous SJW" editor realized the potential threat to stupid and impressionable young readers and made this the straw that broke the camel's back... The Axe is none other than a 100% Saikawa's fault
(1) in a second thought, "The strongest highschooler" is something that shounen has of dime a dozen in all sorts of flavors...
(2) Though Hibari had this gap where his fine with little animals
(3) refer to (1) Shounen needs every badass character it can get... but my point is how Saikawa and Tanaka don't complement each other strenght... ymmv on how many chapters sensei needed to make these two work...