From DSPet at AXA:
In addition to the regular 8 neighbor slots, there is a hidden "9th neighbor" (frozen in storage).
If an NPC moves out of your town, it actually moves to the hidden "9th neighbor" slot. It stays there in a frozen state until you connect to another town (you visit another town or they visit your town)
If you connect with someone (WiFi or DS-2-DS), they will usually swap their "9th neighbors". If both towns are full (8 regular neighbors), then they both stay in the hidden/frozen state. That's how you can get neighbors from distant town you never visited.
For example: Cyrano leaves TownA, stays in frozen state.
TownB and TownC are full up (8 regular NPCs)
TownD has extra room (7 NPCs)
PlayerB visits Town A, PlayerC visits Town B, Player D visits town C
Player D wakes up the next morning to find Cyrano from "TownA" just moved in [even though they never visited TownA or anywhere close]
If the "9th neighbor" slot is empty, the game will randomly pick a new character when it wants to add a new house. That's the case for the initial neighbors or if you never go on WiFi.
In addition to the regular 8 neighbor slots, there is a hidden "9th neighbor" (frozen in storage).
If an NPC moves out of your town, it actually moves to the hidden "9th neighbor" slot. It stays there in a frozen state until you connect to another town (you visit another town or they visit your town)
If you connect with someone (WiFi or DS-2-DS), they will usually swap their "9th neighbors". If both towns are full (8 regular neighbors), then they both stay in the hidden/frozen state. That's how you can get neighbors from distant town you never visited.
For example: Cyrano leaves TownA, stays in frozen state.
TownB and TownC are full up (8 regular NPCs)
TownD has extra room (7 NPCs)
PlayerB visits Town A, PlayerC visits Town B, Player D visits town C
Player D wakes up the next morning to find Cyrano from "TownA" just moved in [even though they never visited TownA or anywhere close]
If the "9th neighbor" slot is empty, the game will randomly pick a new character when it wants to add a new house. That's the case for the initial neighbors or if you never go on WiFi.