Choso (張相 ちょうそう) is not a human. Actually, he is half human and half cursed spirit. Isn’t a cursed spirit supposed to be cruel? No, his heart is full of love for his younger brothers. Especially how he shows his love towards Yuji Itadori (as his brother!) is just… adorable.
Here, you can find why he is the best brother in the world!
Who is Choso?
Choso is one of the Cursed Womb: Death Paintings which is ranked “the special grade cursed material”. So, he, himself was the dead body of fetuses between human and cursed spirit. However, he’s incarnated into a human’s body and now looks like a human.
More details about the Cursed Womb: Death Paintings, see my article↓
He has 9 brothers
The Cursed Womb: Death Paintings consists of 9 bodies of fetuses and Choso is the eldest. For 150 years, they had kept their seals relying on only each other’s existence. Therefore, their family bond is very tight. He also noticed that Yuji Itadori was his brother, too in the Shibuya incident. So, It means Choso has 9 younger brothers.
He always does his best as the eldest brother!
When 3 out of 9 bodies were incarnated into humans bodies forcibly by Mahito and Fake Geto (Kenjaku), Choso swore that they would live for each other.

He tried to avenge his younger brothers, Eso and Kechizu on Yuji (He didn’t know Yuji was his brother yet at the time).

He saw the “not existing memories” of him having meal with his brothers including Yuji in his head and got shocked.
Choso started pointing his anger at Fake Geto (Kenjaku) for trying to make him kill his brother, Yuji because Kenjaku must have known everything.
For more details about Kenjaku → see my article, What Is Kenjaku's Evil Plot? The Reason He Sealed Gojo【Jujutsu Kaisen】

He tried to protect Yuji with full power.
He can’t stop Loving his younger brother Yuji!
After he noticed Yuji was his brother, he couldn’t help caring him. And the way he does is so adorable. He calls himself “oniichan (お兄ちゃん おにいちゃん)” when he talks about brothers. Oniichan is the adorable way to call an elder brother in Japanese; usually little kids say “oniichan” to call their older brother.

Choso wants Yuji to call him “oniichan”. But… Yuji just ignored. Poor Choso.
Yuji: You are our side now. Am I right?
Choso: No!!
Yuji: What!?
Choso: I’m your brother.
Yuji: Stop fooling around!!
Choso: Well, can you call me “oniichan” once for me?
Yuji (looked at the different direction)

When he saw Yuji’s overwhelming power, he went like, “That’s my brother.” But Yuji didn’t believe they were brothers. Again, poor Choso…

Naoya Zenin said Yuji was going to be executed and Choso got mad hearing that.

Choso tried to let Yuji escape from Yuta Okkotsu. He thought, with his plan, Yuji didn’t have to fight with Yuta and also didn’t have to feel bad for Choso for protecting Yuji.
He was like “Ha…What a troublesome he (Yuji) is…” There is a saying “more troublesome the kid is, the cuter they are” in Japan.

When they met up with Maki Zenin, she asked who he (Choso) was. Yuji thought a second and answered he was kind of like his brother. Choso got so excited and went “Yujiiiii!!!”

Choso decided to stay with Master Tengen in Tokyo Jujutsu Tech. As Yuji was leaving, he thanked Choso for helping him. It made Choso cry.
Yuji: Thanks. You helped me.
Choso: …Don’t die.
Yuki Tsukumo: Are you crying?
Master Tengen: ……
Choso: (Leave me alone!)
He is incredibly strong!
Well, Choso is not just a good oniichan but he is strong, too!
The Jujutsu technique he uses is the well-known technique, Blood Manipulation which has been passed down among the Kamo clan. However, his Jujutsu strength is so powerful that everyone who has known the technique surprise; Uraume (裏梅 うらうめ) and Naoya Zenin (禪院 直哉 ぜんいん なおや).
He almost killed Yuji Itadaori in the Shibuya incident (he didn’t know Yuji was his brother at the time.) and Naoya Zenin after the incident (Yuta Okkotsu came in and stopped Choso killing Naoya).
Jujutsu technique
The Blood Manipulation (赤血操術 せっけつそうじゅつ)
The Jujutsu technique which has been passed down in the Kamo Clan, one of the 3 biggest Jujutsu families. You can control your own blood and the materials that your blood is on.
Slicing Exorcism (苅祓 かりばらい)
Using his blood like a long whip, he slashed numbers of people in the Shibuya subway.
Convergence (百斂 びゃくれん)
The technique to compress the blood to the limit. This technique itself is not for attacking, but you can use the powerful techniques with this compressed blood.
Piercing Blood (穿血 せんけつ)
The esoteric technique of the Kamo clan. You release the compressed blood by Convergence from one point. Its initial velocity strengthened by cursed energy can be faster than the speed of sound.
Supernova (超新星 ちょうしんせい)
You shoot a target from all directions with the bullets of the compressed blood. This is the technique Choso had made by his own while he had been facing his technique for 150 years. He used Supernova against Yuji and Naoya so far ant it gave big damages to both.
Flowing Red Scale (赫鱗躍動 せきりんやくどう)
By controlling blood components including body temperature, pulse and the volume of red blood cells, you can strengthen your physical ability. Noritoshi Kamo (加茂憲紀 かものりとし) from Kyoto Jujutsu Tech also used this technique when he was fighting with Megumi Fushiguro (伏黒 惠 ふしぐろ めぐみ) in the exchange event and Megumi called it “doping”.
Flowing Red Scale: Stack (赫鱗躍動・載 せきりんやくどう・さい)
Choso used this technique to complete the blood control inside his body when its control outside body was unable (During fighting with Yuji, Choso got soaked in water and couldn’t use Convergence.)
Choso used it to catch up the speed of Naoya in Shibuya, too. Naoya uses the technique to cut a second into 24 frames and Choso even caught up with the high speed by using this technique.
Blood Meteorite (血星磊 けっせいせき)
The technique to solidify the blood. Though it doesn’t have the speed and power like Piercing Blood, Choso threw it towards Yuji, and it went through his liver.
Blood Edge (血刃 けつじん)
The technique to solidify the blood like a knife. The blood inside the knife is still fluid and its killing power gets higher by circulating the blood at high speed. Choso stabbed Yuji’s foot in close-range battle.
2 more facts that make Choso even stronger
1. Since Choso is not a human, the lack of blood doesn't happen to him unless he uses up all his cursed energy.
2. His blood is poisonous to humans.
10 Quotes full of brother love
1.

Eso, Kechizu, look at me. This is your older brother.
Source: Gege Akutami 『Jujutsu Kaisen』Vol.16
壊相 (えそう) !! 血塗 (けちず)!! 見 (み) ていろ!! これがオマエ達 (たち) のお兄 (にい)ちゃんだ!!!
To Yuji Itadori
In Shibuya subway, Choso found Yuji who killed his brother, Eso and Kechizu. He asked Yuji if they said something before they died and Yuji answered “nothing. But… he (Eso) was crying.” Choso raged to hear it and tried to avenge on Yuji.
2.
You…!! How dare you!! You tried to make me kill my brother, Itadori!!
Source: Gege Akutami 『Jujutsu Kaisen』Vol.16
よくも……!! よくも俺 (おれ) に!!
虎杖 (いたどり) を!! 弟 (おとうと) を!!
殺させようとしたな!!
To Fake Geto (Kenjaku)
Choso realized that Fake Geto was Kenjaku. Kenjaku was the one who made the Cursed Womb: Death Paintings and the vessel of Sukuna Yuji Itadori, which means Choso and Yuji are brothers.
3.
I’ll carry out “oniichan” with all I’ve got.
Source: Gege Akutami 『Jujutsu Kaisen』Vol.16
全力 (ぜんりょく) で お兄 (にい) ちゃんを遂行 (すいこう) する
Note: oniichan is the adorable way to call older brother usually used by little kids.
To Fake Geto (Kenjaku)
Even though Yuji had killed Eso and Kechizu, and Choso and Yuji had a dead battle, now that Choso noticed that Yuji was his brother, so what he had to do was only one thing: to protect his brother, Yuji from Kenjaku.
4.
So what? Is it a legit reason not to stake my life on my brother?
Source: Gege Akutami 『Jujutsu Kaisen』Vol.16
だから何 (なん) だ
それが弟 (おとうと) の前 (まえ) で命 (いのち) を張 (は) らない理由 (りゆう) になるか?
To Fake Geto (Kenjaku)
As Kenjaku dodged Choso’s attack, he mocked Choso and said “Take it easy. You must be tired.” because Choso already had been damaged from the fight with Yuji. But oniichan (older brother) never gives up!!
5.
It’s not a matter of forgiving or not. It’s just how brothers are.
Source: Gege Akutami 『Jujutsu Kaisen』Vol.16
赦 (ゆる) す 赦 (ゆる) さないじゃない
兄弟 (きょうだい) とはそういうものだ
To Yuji Itadori
After the Shibuya incident, Choso was with Yuji. Yuji asked if Choso was okay because he killed Choso’s brothers. Choso answered it was an accident. He is not just strong but very considerate.
6.
You, do you think you can go home alive after you threw a punch at my brother?
Source: Gege Akutami 『Jujutsu Kaisen』Vol.16
オマエこそ 俺 (おれ) の弟 (おとうと) に手 (て) を出 (だ) して
生 (い) きて帰 (かえ) れると思 (おも) っているのか?
To Naoya Zenin (禪院 直哉 ぜんいん なおや)
Naoya Zenin ran into Choso and Yuji. He was looking for Megumi Fushiguro, so he got disappointed that Megumi wasn’t there. Then, he decided to break Yuji’s bone because he was annoying (Naoya is such a jerk!). And it made “oniichan” mad again.
7.
I am the oldest of 10 brothers.
Source: Gege Akutami 『Jujutsu Kaisen』Vol.16
兄 (あに) さ
10人 (にん) 兄弟 (きょうだい) のな
To Naoya Zenin
The answer to Naoya’s question “Who are you?”. Naoya didn’t mean that, but for Choso, being the oldest brother was everything.
8.
But I still have to walk ahead my brothers. This is why I am strong.
Source: Gege Akutami 『Jujutsu Kaisen』Vol.16
それでも弟 (おとうと) の前 (まえ) を歩 (ある) き続 (つづ) けなければならん
だから俺 (おれ) は強 (つよ) いんだ
To Naoya Zenin
Though Naoya got super high speed, he struggled with Choso. Naoya hadn’t met Choso before and of course didn’t know Choso wasn’t human either. So, he wondered why this guy was so tough. Choso’s answer was that he had to be a role model for his younger brothers. If he walked a wrong way, they could choose another way, if he walked a right way, they could just follow him. And for that, he kept making mistakes to show the ways for them.
9.
Sorry, but I can’t understand your feeling that you couldn’t love your brothers.
Source: Gege Akutami 『Jujutsu Kaisen』Vol.16
悪 (わる) いが兄弟 (きょうだい) を愛 (あい) せなかった
オマエの気持 (きも) ちは分 (わ) からん
To Naoya Zenin
As you know, Naoya is a jerk. He looked down everyone and believed he was the best. Of course, he even looked down his brothers and didn't think they were worth living. This is the line Choso said right before he gave a dead blow to Naoya.
Naoya, who thought he made what he was now by himself and Choso, who knew he could be how he was because his family was there. Naoya was overwhelmingly strong, but the difference of their briefs must have been the game-changer.