@elfalas
A prostitute walks up to you and says "BJ behind the house for $10".
You pay her $10 and go out back.
Cops are waiting for you out back. Looks like a prostitution sting.
In the immortal words of Marion Barry "Bitch set me up!"
Who goes to jail? The woman working on the prostitution sting or the guy who took the proposition?
To make it simple. He set himself up. He didn't have to accept her offer. Especially since there was no reason for him to go with it anyway.
Look at his situation.
One woman, that he likes, lets him get away with constant sexual harassment. Even from his point of view it should be obvious that she isn't totally against being with him if he cleans up his act. He just doesn't want to clean up his act. The fact that she doesn't do more than scold him occasionally re-enforces his behavior in some ways since he knows he'll get away with it.
One girl who definitely likes him who will grow into a fine yandere one day (yes she's too young for him).
One woman is a "friend with benefits" who may not be looking for a long term relationship, but certainly doesn't mind a bit of fooling around off the record.
One partially converted tsundere and friend. Yes he can and should avoid this one at all costs, but he won't if given the opportunity and you know it.
After having all of these options he still chases after an unknown girl who randomly propositions him without thinking twice about the situation.
As for her side of it, she hears all of this talk about a guy she assumes is her sisters boyfriend and what's the first thing she sees him doing? Hanging around with the boys as they try to pick up women.
Also they loudly proclaim in public that they want to touch boobs. Yes he didn't say it, but from her point of view she sees them together trying to do the same thing. So she gives her potential brother-in-law a simple test. "Is he true to my sister or will he go after anyone".
She even directly asked him "were you trying to pick up random girls on the street"
Which he says "no, it was just those other guys".
But what is she to him at this point? A random girl on the street.
What did he do? Got together with her on his first opportunity.
What are you suppose to think of that first impression of someone who you assume is dating your sister?
I think Aria is justified in her actions, but I also think nothing serious will come of it anyway. Elise knows he'll hit on any woman with a pulse and she feels she owes him for saving her fathers clinic. So overall nothing major is going to happen... well except Aria potentially being added to the Harem if she sticks around.
Also lets look at the harem stereotypes we have filled right now:
Elise - "first girl" you can consider her the childhood friend of this story. Class: White Mage
Luluca - flirtatious second girl, but the first one actually introduced. Class: Thief / Rogue
Fran - Tsundere violent man hater Class: Black Mage
Sera - Ara Ara onee-san Class: Archer
Yuelle - cute loli Class: Fighter
We have room for an imouto character who also can act as a Tank. She's a good addition to the party as it currently stands.
Plus for a perverted MC Shiki is pretty weak sauce. Sure he stares at and hits on random women, but he's only molested two, Luluca and Elise (mostly Elise since Luluca has been consensual). He doesn't touch loli and isn't interested in Flat Justice so Fran is out. Fran has been running block for Sera. That along with Luluca's assertiveness has keep Sera out of arms length. He'll need to step up his game to earn his title.