gloss

It is a completely new word created by the production team to describe part of Gojo's life. At the beginning, even Japanese fans had a hard time understanding what this word means. However, after Vigneravan's (the video producer) tweet, it is confirmed that 「融独」 is related to 「親友」/shinyuu/bestfriend. Gojo only has one and only one bestfriend, so this new term points to Geto.

The producer says "a bestfriend is a 'toxic' and 'melting' existence" when talking about Gojo's bestfriend, Geto. There is a wordplay here: both "toxic" 「有毒」[1] and "melting" 「融独」 spell the same way, "yuudoku". This fact is actually realized by fans in the way they assume how these characters are spelled when parts of them are used within other more common terms (especially when the referred term doesn't exist). 「融独」 is a combination of 融 (fusion/melting) and 独 (loneliness) - in literal sense, it means "melting the loneliness". In other words, the video producer's interpretation is "Geto, Gojo's best friend, is like toxin to him, but at the same time he melts away Gojo's loneliness".

Let's go back to Gojo's tribute video. This video starts with Gojo's birth, his youth, then his days as a teacher, and ends with him joining the battle with Sukuna, and finally going to the airport in the afterlife. Out of 11 hours, Geto appears in nearly 5 of them. The common vibe of the video is Gojo's happy moments with his friends, colleagues, and students. If you notice, there are NO scenes where he is fighting or in danger. The only distressing moments in the video are: when Geto becomes depressed, when Geto leaves Gojo, and when Gojo is left mulling in his own thoughts afterwards, sitting right where his bestfriend used to:

This means that the saddest and most depressing thing that ever happened to Gojo's life is when Geto left. And we all know how Gojo never forgets about him, and in fact, delays the time to execute Geto by order, only going down on him when Geto declares war 10 years later. This can be interpreted as part of the video producer's view, "toxic".

Yet, Gojo doesn't let Geto out of his mind. At the start of the video, after the images of him as a baby, Geto is the first person to appear in Gojo's life:

The above image gradually adds Yaga and Shoko afterwards. You can say that Gojo had no significant memories as a child, because he was born with powers and expectation, and thus, as a lonely kid. Meeting Geto, he has the first ever friend, an equal, someone who can understand him. So the memories when he first had Geto in his life, also indicating the start of his 3-year treasured bluespring, is when he finally turns from a lonely child to no longer lonely.

Yet when he loses Geto, he's become lonely again. Note that, Gojo has never been "alone", but he has been "lonely" (there has been many analysis for this, from Shoko's thoughts about him right before he gets released from Prison Realm, and in c236 when he confesses). Which turns out, Geto's existence is too big for him. Isn't it unhealthy to give so much leeway to an enemy, "the worst curse user of the jujutsu society", when he's supposed to execute Geto as soon as possible before he becomes a big threat? Yet, whatever Gojo has for Geto is too much and enough for him to give Geto freedom until he can't anymore; and after that, Gojo still wishes Geto had been there to pat him on the back before the fight with Sukuna, in order to fully feel satisfied. To wish for something impossible as an existence of the dead, who was supposed to be an enemy but wasn't.

It is "toxic", but Geto is exactly the only thing that can "melt his loneliness". That is why Gojo, who's been lonely all his life being the strongest, cannot let go of Geto in his mind. Geto has been the first one to make him change for the better, to stand by his side despite his status and origin, and even though he left, he's still Gojo's main source of inspiration to build his dream of changing the jujutsu system for the better, and to not let children fall for the same fate as his best friend once did, preserving their youth. Despite all the unfortunate events, Geto still stays as the special "toxin" to Gojo, the only one that can melt away his loneliness, the only person whose existence brings him satisfaction. (there's a whole topic on how the word "satisfaction" Gojo uses to describe his feelings when fighting Toji or Sukuna and the one used when describing Geto below are 2 similar terms with different connotations, but I'll leave that for another time)

For our own assumption, it is also likely that Gege Akutami is the one to come up with this word 「融独」. As the author who created Gojo and Geto as a contrasting pair, he is the one who understands their relationship the most. But mostly because he's one of the few people (involved in the series) who has deep understanding of Japanese language and often plays around with words. JJK very often includes highly complicated Japanese words and terms (even for Japanese readers), so for him to come up with a completely new word to pay tribute to Gojo is not out of possibilities.

And it leaves you in awe again how important Geto is to Gojo.

Watch the 11-hour tribute video:

P/s. by coincidence (or not), Tatsuya Kitani, the singer/songwriter for JJK Hi/pd arc's OP "Ao no Sumika", includes "Love Song" in the album Ao no Sumika. And this song is... well. A bit familiar.

Would the song somehow reminds you of how the video producer perceives Gojo & Geto's relationship? It's up to you.