jk one more theory before I go lol
The more I think about the past!Lavi becoming crown clown theory the more sense it makes.
1. At first, Allen couldn’t even move his innocence hand (as if it were a prosthetic added onto his body). Then, after he activated his innocence, it was incredibly unstable until he decided to stop fighting to die and start living for people and akuma, AKA he decided to start fighting to live period. After he made that declaration, he aligned more directly with his innocence’s wishes—Past Lavi’s wish for him to live! So his synchro rate increased.
2. Lucia mentioned that Past Lavi had shimmering silver hair just like our Allen’s. Our Allen mentioned his hair was chestnut until he activated his innocence. In a komui’s corner, Timothy explained after his hair turned green once his innocence activated, Allen told him his also changed color and he once tried to dye it, but it just changed back to silver—the same color as Past lavi’s!
3. Crown clown is unique in the ways it’s a defensive and offensive innocence. It has a white cape that wraps itself around Allen to protect him just like past!lavi once did for past!allen.
4. Of course, this is the most obvious point and one many have mentioned—crown clown actively protects Allen. It mended his heart post-Tyki and it plugged the wound Allen got from Kanda. Aka, it does everything it can to protect Allen.
Now I’m super on board with this idea. Especially because it also explains why Neah may have thought of past lavi when he saw Allen’s reflection for the first time AND why he seemed so bugged out by it. Aside from the whole Allen being young thing, since Allen has Past Lavi’s hair, his reflection likely gave Neah quite the jump-scare since our Allen looks like Past Lavi and Past Allen put together. And the last time Neah saw them both he probably saw them off before they traveled together. Which is also why he may have figured Allen had been reformed by apo!