Skeleton Knight in Another World Season 2 Episode 4 starts in quite a creepy way, as a little girl is shown to be petrified in front of an old door in a creepy mansion. The mood has been set for a chapter that contains family reunions, sibling rivalries, and a slowly building mystery surrounding the question of an abducted captive.
The main thing that happens in Skeleton Knight in Another World Season 2 Episode 4 is that Ariane meets her older sister Eevin, and follows it up with a defeat in the sparring match against Eevin, while the gang finds out about the horrible secret of a sanctuary designed to save elves and beastfolk.
Eevin Puts Ariane and Arc to the Test

Ariane and Arc set out to meet Eevin, who is famous for being a sword fighter. Their trip is interrupted by a hooded person who attacks them, only for Ariane to discover that the attacker is Eevin, who was testing their reflexes before embracing them warmly.
After some chatting, the sisters get to know that Eevin already learnt about Ariane’s curse and Arc’s real skeletal nature from their mother. Eevin also informs them surprisingly that she is going to get married, which adds another funny moment to this episode of Skeleton Knight in Another World Season 2 Episode 4 before the training duel begins.
A Humbling Duel in Skeleton Knight in Another World Season 2 Episode 4

Eevin dares Ariane to have a spar to see her improvement, but even with Ariane’s much better skills, she is still unable to hit her opponent. Eevin's incredible speed leaves both Ariane and Arc dumbfounded as the distance between the two right where they are is still far too wide.
Later, Arc tells an upset Ariane to cheer up and look at the achievements she has made compared to her starting point. She reminisces about the moment when Eevin saved lives in her childhood and realizes this is where her motivation to train like crazy during the Skeleton Knight in Another World Season 2 Episode 4 comes from.
A Royal Rivalry Simmers in the Background

Meanwhile, Princess Yuriarna comes back to her brother Sect after surviving an assassination attempt. She informs him she has been successful in concluding a trade agreement with the elves, acquiring a diplomatic achievement that boosts her standing in the kingdom.
Sect commends Yuriarna in front of everyone else but actually wonders about how she managed to survive since he has his own agenda of getting rid of her from the line of succession. This plotline increases political competition in the series, suggesting that the rivalry of the two siblings will become even more intense in the future.
Lady Sanctuary Hides a Dark Secret
The mystery of why Eevin is calling Ariane comes into light. The village of Daniel has Lady Sanctuary, which is an asylum for rescued elves and beastmen run by the benevolent Lady Liza, but anyone who enters the residence seems to disappear.
Ariane, Eevin, and Arc unearth the truth as they discover Liza has been missing, thanks to her husband. They come across a room that is sealed, and there is something evil about it. When they get through the room, they are attacked by a troop of skeletons, thus bringing an end to Skeleton Knight in Another World Season 2 Episode 4.