The Wondrous Pouch debacle was the last straw that got Pippa expelled.
It seems odd that the Astral Academy would entrust her with their
Bag of Holding after her expulsion, so it likely happened while she was still attending. Pippa tearing a hole in said bag, failing to notice it, and losing the seeds means that she not only destroyed a rare and powerful magic artifact, but
very likely doomed part of the Wilders' habitat to rotting into desert. Even though it was an accident, this would still obviously be a gravely serious offense.
Joker was able to get to Esperia through the Super Smash Bros. universe.
Joker and Queen are the only Dimensional heroes who are given no backstory on how they got to the world of
AFK Arena. After getting his invitation to
Super Smash Bros. Ultimate, Joker would find himself in a universe directly connected to countless other universes. With how many crossovers have happened between other members of the
SSB cast in recent years (such as
Mario Kart 8), it's possible that traveling between franchises is a thing that happens through that medium. And it just so happens that fellow Smash fighter
Young Link has
been to the same universe that fellow Dimensional hero
Ezio Auditore would
also end up in, so a line of connection is there.
Annih is trying to get his hands on Soul Edge.
There are numerous connections between
AFK Arena's Dimensional faction and the
Soul Series. As pointed out before, Ezio had been stuck in the
Soul universe prior with no canonical explanation in
Soul Calibur V. In addition, the
Samurai Shodown characters Nakoruru and Ukyo ended up in Esperia, around the same time that Haohmaru from the same series was transported to
Soul Calibur VI by
Soul series
Big Bad Inferno. Furthermore, one of the known canonical wielders of Soul Calibur and the founder of the
Soul series's Aval Organization is none other than
Arthur. Lastly, hidden in the data is that Soren is referred to as "SoulCalibur" in the internal game files due to his being a
Living Weapon.
The malevolent God of Death in the possession of an all-powerful sword that devours souls would doubtlessly bring all resistance to a swift and tragic end. It's possible that either Annih is trying to force his way through to the Soul universe by tearing open dimensional rifts like he's known to be doing, or Inferno has made a deal with him: seek out a suitable host among the worlds — which would explain how he got in touch with Haohmaru — and he'll wreak his havoc on Esperia in exchange.
As a note, this WMG was added before Geralt — a character who is in SCVI's playable roster, not merely sharing a universe — was added to AFKA, strengthening the connection even further.