The Man Before

Before we discuss Tengan as the chairman of Future Foundation and mastermind of the killing game, it's best to understand his origins and where he came from.

Tengan was formerly the headmaster of Hope's Peak Academy before being succeeded by Jin Kirigiri, afterwards becoming the school's advisor. This is the first instance we see of a core trait of his, that being his distaste for conflict.

In his artbook profile, his dislikes are listed as just "conflict." His personality description reads:

"Former headmaster of Kibougamine. A good-natured old man who currently works as an advisor at the school. He understands what the academy is aiming to do, but questions if it’s true hope. He wants the main and prep school students alike to enjoy carefree school lives." -Translation Source

Tengan wants everyone to live a carefree life free of conflict, this is what hope is to Tengan. As an advisor, Tengan is able to voice his opinions on issues regarding school, particularly ones about the school's vision and ideology.

Tengan believes that hope comes from a world without conflict, one of peace. To him, conflict just creates despair.

Tengan questions many of the decisions made by Hope's Peak, and is personally against the Kamukura project. However, as just an advisor, he never forces his hand and gives Hajime the choice of whether or not he wants to participate on the project on his own. This ties into Tengan's core trait of hating conflict, allowing Hajime to make his own choice but still trying to persuade him into making a certain choice.

The Tragedy

Unfortunately as every one knows, Junko's plan succeeded and the world was plunged into despair.

Tengan made the decision to stay outside of Hope's Peak and help fight against despair, doing whatever he could in order to end the conflict.

The war began to take a toll on Tengan. He knew that all the fighting that the Future Foundation couldn't end the war. After all, violence creates more despair.

When Kyosuke asks Tengan why he changed, he simply responds with "Because I learned the way that we're doing things now will not eliminate despair."

Now the question is, how exactly did Tengan change? What made him become a "coward?"

It's revealed that before the killing game, Tengan obtained the despair video and watched it by his own volition as a last ditch effort to end the war. He knew that the conflict wouldn't end just by constantly fighting, so in a way this was him giving in. And with that, the old Tengan was gone, and he became another Remnant of Despair.

The Man After

Despite being brainwashed and having his mind reconditioned in the same as Class 77, he didn't align with their goals nor was he even a part of them. While his mind was twisted, his core traits and ideals remained.

It's worth noting that being brainwashed doesn't completely change who you are as a person. Just like how Nagito obsession with hope remained as a remnant, Tengan's desire to end conflict remained as well. The difference is that their methods became more extreme and subconsciously reflected despair more than hope.

As despair Tengan, he would go to whatever lengths it necessary to achieve "true hope," or in his eyes, peace.

In Danganronpa Gaiden, Tengan tells Kyosuke to let Misaki and Takumi decide what they want to do.

However, Tengan slips a bomb into Misaki's pocket as an extreme measure. As despair Tengan, he didn't lose the side of him that lets people choose what they wish to do, what changed is his method of persuading people getting more extreme.

The Final Plan to End All Conflict

During this time, Tengan began working on the plan that would end all conflict and despair once and for all. The war wouldn't end the way things were going, and more fighting would pointless. However, the perfect opportunity fell into his hands.

Tengan had discovered that Ryota not only developed the technology used in the Despair and Suicide videos, but that he was also working on a brand new Hope Video as well. With this, Tengan could put an end to the war once and for all.

With his immense power in the Future Foundation, he was able to make changes to the building in order to set up his very own automated killing game. He would take advantage of Makoto Naegi's trial to bring the top members of Future Foundation in one place, only to gas them and trap them in a killing game. Through word of mouth, Ryota would discover the killing game and release the Hope Video in order to end everything. Why did he choose to do it like this instead of just stealing the video? Well, it's pretty simple.

Looking at it realistically, tension was already brewing amongst Future Foundation. The chances of someone like Kyosuke who already wanted Tengan dead getting in the way were too high, so getting them out of the way so that way they can't affect his plan was important.

More importantly though, he wanted to give Ryota a choice. As we saw with the board of trustees, Hajime, Takumi, and Misaki, Tengan wants people to choose what he believes is true hope on their own. However, he's not opposed to persuasion, and as despair Tengan, his methods have only gotten more extreme. Obviously Ryota wouldn't possibly say no in a situation like this, and that was Tengan's plan.

Unfortunately Tengan made one mistake, Ryota showed up to the meeting uninvited. Unfortunately the word of mouth that Tengan intended to use to get Ryota to discover the killing game ended up causing Ryota to find out about the meeting and go there.

Unfortunately, once the gas was automatically released, Tengan couldn't just cancel the killing game, and it would be suspicious if everyone but Ryota vanished. As a result, he had to bring Ryota along with them and give him the wristband that was meant to be used for Yasuhiro.

The wristband prevented Ryota from using his talent, which may seem backwards on the surface, however it makes more sense when you think about it. If Ryota used his talent to make everyone stop fighting, then that would completely screw up the killing game.

So Tengan opted to protect Ryota until the killing game ended, and when he died, he left a message for Ryota inspiring him.

It's worth noting that Tengan didn't intend for the killing game to last forever. He knew at some point they'd regain connection with the outside world or discover the breaker room, which he intentionally hid behind an exit door to bait people to it. His plan was just to have it last long enough for Ryota to release the Hope Video without anything getting in his way. But now with Ryota with him, his plan shifted to protecting Ryota until the game ended.

But things were different now, Tengan was affected by the virus known as despair. Whether he was conscious of it or not, his plan to get rid of all conflict, to eliminate all despair, was just another form of despair in itself. Tengan's plan would inadvertantly bring more despair than hope.

And that is the very nature of Kazuo Tengan's plan! (dun dun dun)

So Basically

Tengan was a man who believed that true hope came from peace. His distaste for conflict was the driving force for many of his actions. While he encouraged people making their own choices, he aimed to persuade people into picking what he perceived as true hope.

When he was brainwashed as a result of his own desperation, his methods became more extreme and twisted and he didn't even realize. He believed that everything he did was for the greater good, to end all conflict, even if he had to manipulate people and go to extreme lengths to do it.

That's why Kazuo Tengan is such a great mastermind. In the end, Tengan's goal was to end all conflict and create what he thought was true hope. However his nature as a despair betrayed him, and unbeknownst to him, he would actually be creating another form of despair.

Conclusion

I feel like a lot of people underappreciate Tengan. In my opinion, he's such a cool character and belongs next to Junko, Izuru, and Monaca when discussing the masterminds of the Hope's Peak saga.

If I were to try to guess what caused Tengan to be so disliked, I'd say it has to be due to the quality of the dub which makes him more difficult to understand along with Danganronpa 3's (honestly undeserved) reputation in general.

There's a lot of really cool things about Tengan, like just how awesome it is that he's an old man with his chuusen. But unfortunately, he's just seen as the forgetable funny old guy from Danganronpa 3.

Maybe with this thread I was able to persuade you into reconsidering. However, in the spirit of Tengan, that's a choice for you to make. I'll still give my input though :)