Let's take a look at how two different anime character types would handle a similar situation. Should a woman stumble into the men's locker room by mistake, accidentally catching a glance at her senpai without a towel, a tsundere woman may run screaming for the hills slating him as a pervert.

However, an older more experienced woman, when presented with the same situation, may lick her lips and act surprised while uttering a sarcastic Ara ara. Ara Ara is used to not only imply surprise on behalf of the speaker but to give the implication that they like what they see and would be interested in seeing more of it!

The phrase itself does not have an origin per se, as it is merely an exaggeration of traditional Japanese. In Japanese, the phrase "Ara" is often used by women to express surprise (in a similar fashion to "Oh!"). This holds no correlation to anime but perhaps the addition of a second "Ara" is supposed to imply sarcasm.

A single "Ara" is used to express mild surprise. Perhaps this was the inspiration for the sarcastic ara ara, implying that those who use it are only mildly surprised by what they see (whereas others would be positively horrified or embarrassed by a similar situation). Ara ara is used in everyday Japanese but virtually never to the same effect as it is in anime.

Re:Zero is an isekai anime focusing on protagonist Subaru. After being transported to another world, Subaru learns that he has the unique ability to rewind time after suffering fatal damage. Subaru will revive after being killed at a checkpoint he has no control over. Wanting to learn more about his power and explore this new world, Subaru does his best to help his new crush Emilia in her electoral process.

Along Subaru's road to the top, with a power like his, one thing is for certain. He's going to be dying a lot! One of the very first roadblocks on Subaru's adventure is Elsa Granhiert, an assassin working for a mysterious organization. Much like other ara ara characters, Elsa uses this phrase to punctuate her sarcastic surprise. This is done by either teasing her prey before she goes in for the kill or taunting those who try to intimidate her. Garfiel and Subaru's hurtful insults are brushed aside with a mocking ara ara as she clearly sees them as no real threat. Even when Ram slices her arm open, Elsa (instead of panicking) licks at her wound before exclaiming "That hurt. I thought I was a goner." Ara ara energy does not always have to be romantic in nature. The true nature of ara ara comes from sadistically teasing those in your vicinity (much like Elsa does throughout the series).

Issei is a typical high school student who wants nothing more than to find a girlfriend. After finding a seemingly nice woman who agrees to go on a date with him, he discovers she is an angel and is murdered in cold blood. Luckily, he gets another shot at life after Rias Gremory, a high-ranking devil, revives him as her servant. Now, Issei fights alongside Rias in the war between angels and devils.

Issei is a bonafide horndog and his advances are not always met so receptively. Rias, Asia, and Koneko are often embarrassed or agitated by his constant remarks. However, when it comes to Akeno, Issei seems to have met his match. Akeno appears more than willing to indulge Issei in whatever fantasy he has concocted and expresses her surprise and delight with Issei's suggestions with her patented ara ara. It is then Issei who cannot keep up as Akeno's experience starts to take over. Dissimilar to Elsa, Akeno's prey is not one to be mercilessly killed but similarly to Elsa, Akeno implores the same sarcastic ara ara teasing tactic to get into her lover's head.