The newly-added characters from the Ultimate expansion are the following (listed by when they are unlocked):
Chapter 6: Achilles, Joan of arc, Yang Jian, Ryu Hayabusa
Chapter 7: Gaia
Collect all Perseus Fragments: Perseus
Chapter 8: Hades
To verify if you have unlocked a Bond event, go to Gallery>Officers>(select character)>Lines>Camp Events. It will list "New Companion - (character name)" and "Bond - (character name)" for each other character that you have unlocked a conversation between those two characters.
(If you do not see the Camp Events option, you haven't unlocked any for that character.)
You need to unlock all of the Bond entries for each of the characters listed above. To do so, you will need to also max out the bond-meter for each of the following characters: Xiahou Dun, Cao Pi, Lianshi, Zhong Hui, Sanada Yukimura, Hideyoshi Toyotomi, Taigong Wang, Sun Wukong, Yoshitsune Minamoto, Sanzang, Zeus, Athena, Odin, Loki
Once each of the characters added in Ultimate and the conversation partners have their Bond meter maxed out, you should be able to view all the interactions and get the achievement.
As such, this is best done passively over time as you unlock some of the characters very late on. So just make sure to get each of the characters involved to have a max Bond meter and you should get this without much issue.
Credit: Compiled information from the comments in this thread: https://steamcommunity.com/app/831560/discussions/0/17422683...