Dumpsterfire

Antinomy is the one talking the whole time. But there’s a change of pov in the visual presentation. The "slideshow" portion where Antinomy explains what happened to the future is still his perspective. But from where he talks about Aporia’s despair and three personas, the visuals start to shift to Yusei's perspective.

By the time of “My mission was to protect you and help you grow,” the shot of Bruno’s face is entirely from Yusei’s pov. What I want to point out is: what’s on screen here isn't necessarily Antinomy’s actual attitude; it’s how Yusei is perceiving/imagining him in that moment.

Then Antinomy says: “I never expected you to have evolved this far. And to think, it’s on me to cut it short. ”

Yusei: “Am I just a gear then?” (Side note: The use of the "gear" metaphor feels like a deliberate callback. Yusei must have taken to heart what Bruno said about being "gear that turns your dreams" when they first met. )

At this point, the conversation still seems to be about whether Antinomy/Bruno was ever sincere. The cold, aloof expression of the imagined Bruno is just hostility for being on opposite sides. However, there’s a very similar frame in the final battle against Z-one, which suggests something else. There, Yusei “hears” (imagined) Bruno’s voice: “Yusei, you will surely find it—your own accel synchro,” followed by his thought, “Bruno, I found it.” Then, we see the imaginary Bruno smiling.

These frames are clearly Yusei’s mental projections. One could interpret it moderately as Yusei thinking that Bruno was worried about him, and the final smile is a sign of relief. What I find more plausible (and unflattering), however, is that the unsmiling expression in the first two frames represent the internalized Bruno as a member of Yusei’s "inner committee" (the 6's inner authority), with an attitude of appraisal/scrutiny. The final smile isn't relief; it’s approval that Yusei has met the expectation. Furthermore, this interpretation only makes sense if Yusei does regard Bruno/Antinomy as more of a guide/mentor than a friend/equal comrade. After all, it’s 5ds, not GX. 

This is classic 5 behavior when they feel insecure, or uncertain about their understanding and calculations. They don't want to discuss with others because others’ emotions and opinions interfere with their thinking process. They’d rather figure it out on their own first and then just present the result to everyone else as a done deal. This explains why Antinomy kept his regained memories a secret even while acting as, and believing himself to be, a 5D's ally. By the way, this 5-style secrecy works almost seamlessly with Bruno’s 9-style "playing pretend", effortlessly driving things to the point of no return before anyone else realizes.

2. He likes to watch from behind the scenes. Let’s not forget that, while Bruno is at the front end interacting with 5ds, Antinomy is (almost) always at the back end watching. Even when he himself interacts with Yusei, he tends to adopt a "poke and retreat" attitude—it’s less about telling Yusei what to do, and more about probing Yusei for reactions, especially for those that exceed his expectations. 

This neutral, holding-off stance is maintained on a larger scale: he executes his mission to fulfill his vow to Z-one, while simultaneously putting his lot on Yusei, all while hoping that Yusei’s triumph could assure Z-one and free him of the burden of saving the future. He likely anticipated all outcomes. He could genuinely say “I started the duel to show you a new power”, while having also (mentally) prepared for the possibility that Yusei might emerge victorious. (This indecisiveness, IMHO, is also the 6-wing's suspicion leaking in). 

3. The so5’s "totem": Here totem refers to an abstract, sublime ideal, which often also entails some source of power. The so5s compensate for their internal sense of depletion by attaching to this sublime being, while simultaneously becoming even more acutely aware of their own inadequacy by comparison. (“I felt ashamed watching Z-one fight without losing hope even in despair.”) The totem is usually non-human, but can be projected onto people (like the aforementioned victim, who is not entirely innocent). A classic pitfall is "Loving humanity in the abstract, but struggling to love concrete individuals." Real people — including, of course, themselves — can end up being sacrificed for the sake of the sublime ideal.

The social instinct combined with a 6-wing also brings out some so6 traits, like a rigid sense of duty and loyalty to a faction. (“I am tied to Z-one and my comrades by unbreakable bonds born of despair. My vow to Z-one is my mission.”) Even when he doesn’t necessarily agree with the faction’s ideology/objective—and is really sort of off doing his own thing—he still feels this “imperative” to go down with the ship alongside old comrades.

4.The totem for Antinomy is “clear mind”, which is courage, or the overcoming of fear. Fear of the enemy’s strength, fear of failure, and for Yusei, the fear of failing others' expectations and being abandoned.

Little desire for isolation: He literally has no personal space and seems completely fine with that. The only time he ever asks for alone time is Ep 103, when he’s having a memory flashback. Otherwise, he’s pretty much down for whatever nonsense the group is chasing after. It doesn’t even take that long before he naturally slips into a shared peace-keeper role with Crow (and becomes a bit of Jack’s punching bag, which inevitably annoys me). The extent of his active participation in the group makes me think he’s a so9.

Sincere humbleness (humility): as in, “want to be a gear that helps turn your dreams”. And a longing to belong, like the scene where he wanted his name included in the team name. He also gives off this soft, innocent, and clumsy aura, which I think is significant, since 5s typically don't want to be seen as too innocent, as it implies vulnerability. While 5s probably also don’t want to be seen as aggressive, their defensive, wall-building tendency can make them look hard, or arrogant (see, e.g., Antinomy).  

"Pretend Everything is Fine": As Bruno gradually recovers memories of Antinomy and Z-one and the past, he never discloses any of it to Yusei and others; he just keeps acting like nothing happened. He seems to be waiting for Yusei to steer the wheel. While Bruno and Antinomy share this secretive/un-transparent tendency, it could be from distinct motives. For Antinomy’s (E5), it’s more like “I don’t have sufficient information (memory) yet to act”. For Bruno (E9), it’s more like "only Yusei can save the future, so there’s nothing for me to do but wait".

Some Enneagram-informed interpretation:

E9s fear losing connection with others. Thus they neglect, or forget about, their own dissatisfaction, upsets, needs and wants, so as to avoid conflict which could break the connection. Although Bruno is an amnesiac persona, his subconscious might have retained the feeling of losing everyone in the apocalyptic future/past. He seems to side with Yusei, but also doesn’t want to break with Z-one and other old comrades. He can’t disclose what he knows, since that essentially means choosing a side, i.e., putting himself on the opposite side of old friends. His expectation of Yusei is both for Yusei to save the future, and for Yusei to make the choice for him. In the final duel (144-145), even though Antinomy is technically the one on screen, the theme of "Bruno" remains: Yusei, (under Antinomy’s pressure) by declaring “I’ll defeat whoever stands in my way”, saves Bruno from the impossibly hard choice between his two worlds.

9s also have a tendency for self-erasure, to blend into the environment to avoid friction against it. In this sense, Bruno doesn't seem to feel at ease with, or “entitled” to, his own existence. He likely can see from Antinomy’s perspective, where "Bruno" is a mask. Better (or worse) yet, because "Antinomy" himself doesn’t have long to live anyway. Then it’s a completely logical position for a dying person to take: to cherish what time he has left and keep the memories as happy as possible. 

Guesses from Enneagram theory:

Childhood: There’s a Enneagram theory which says that in childhood, or before stress/trauma, people look like their integration point. In particular, 9s integrate to 3 (confident, proactive, competitive). And Johnny, from the very brief glimpses we have of him, indeed has a high-energy 3/7 vibe before destruction.