What is "ecchi" anime ??
Ecchi anime is an anime type that uses heavily sexual tones, suggestive themes, partial or frontal nudity (frontal is usually not the ecchi anime aired on tv, the frontal nudity ends up on DVD/Bluray release) without actual sex taking place a lot of times the male main protagonist is placed into a harem like situation (while there are also girls with boy harems in ecchi anime I personally do not watch them). When an anime goes that far, when sex actually occurs, we call that hentai, which we associate with anime pornography. These splits in definitions between the two is a Western thing, I won't get into it because I'm no expert but it's not the same overseas. If you feel like getting into definitions and words and how they are different I suggest doing research and asking people from the country what they know. These are just the genres that we have grouped these type of anime into.
So why has it gained such popularity recently ??
Well, I believe that a lot of it has to do with the style of anime they combine it with, because as I mentioned ecchi is a sub-genre of sorts, combine it with a main genre like romance, sci-fi, comedy, and you have something unique. People like sexual things, sex sells lets be honest, just because it's anime doesn't mean that it's different.
A great example of something incredibly odd, unique, funny, with proof of this is a new manga & anime series. Monster Musume: Every Day Life With Monster Girls. In it, humans and monster species have finally begun to co-exist but many monsters stay with families to help them adjust to human life. Main protagonist Kimihto Kurusu, is accidentally given a monster girl, a lamia (half snake, half girl) named Miia, to look out for. Long story short more and more monster girls end up staying with him and he becomes the first test case: if monster girls can live here now, why can't they marry human males?? So he's given a choice.......pick one and marry them......which is where all the comedy ensues. It's funny and never takes itself seriously, it knows it's an ecchi anime and plays purely on "fan-service" (T&A) and because it never takes itself seriously and it's funny it is an anime whose popularity has skyrocketed since it started.
So considering I said it was so difficult and that shows like Senran Kagura fall flat trying to bring plot to ecchi anime, it seems impossible right ?? To answer honestly, most ecchi anime are fluff and pure fan-service and you really shouldn't expect a plot going in at all anyways. Essentially, let's toss out a main character and surround him or her in ridiculous situations with a harem of girls or guys that eventually all falls in love with them and make sure it's as sexual as possible, fill it with T&A, and BAM fan-service to the max. That is the typical ecchi anime and there's no plot really.
However, I've found one solid example of an ecchi anime with a good plot. Which if you look at the characters designs and see maybe one episode of the show or read one volume of the manga you'd say "ya this can't have a good plot, it's just a high school boy as the main protagonist having his biggest fantasy come true". Surprisingly in the 3 seasons it's had, with a 4th coming, it has been very interesting with a good plot and despite the ecchi/harem anime vibe it has it's managed to create good characters which is odd for it's style of anime. That anime is: High School DxD
So, main protagonist Hyoudou Issei, is along with his two best friends despised by most girls at their school as just these huge perverted guys. After meeting a girl who actually agrees to go out with him, they have a lovely date, then she kills him.......turns out she was a fallen angel. He is revived and brought back to life by one of the upperclassmen and president of the school's Occult club, Rias Gremory, who he had no idea was a demon let alone the younger sister of the Devil himself. So she takes him into her "household" along with other people at the school he had no idea were demons: the school's resident pretty boy: Yuuto Kiba, the Occult Club Vice President: Akeno Himejima, and other club member: Koneko Toujou. Basically everyone in the Occult Club was a demon and servant of the Gremory family. Everyone has a power except Issei but when rescuing a young girl of faith named Asia from the fallen angel that killed him he receives his Boosted Gear, his power, unbeknownst to him and everyone else initially this is the power of Ddraig the Red Dragon of Power (or the Great Welsh Dragon) and with that power comes not responsibility.......no it comes with rivalry, for as long as there is a Red Dragon there is a White Dragon and the two nearly destroyed the world once. It took the combined powers of the demons, fallen angels, and angels to stop them. Issei ends up having to use this new power to rescue Rias from being forced to marry a rival devil family member Riser Phenex, he destroys him by reaching a new understanding of the power he shares with Ddraig.
Slowly over time, two members of the church are sent to "investigate" the Occult Club, knowing they are demons they are suspected of heinous things in the area. One of them, Xenovia Quarta, becomes a demon which disgusts her best friend thinking she betrayed Heaven when actually it's because she discovers that the people causing the suffering were a priest and an exorcist and was told by Archangel Michael (of the Christian faith) that God was dead, he died during the last demon/angel/fallen angel war. Hearing that, Rias and her group were the only ones she could turn to in order to help her deal and adjust to this revelation.
Michael of the angels, Lucifer of the demons, and Azazel of the fallen angels find that it's best to keep the peace in order to prevent something similar from happening again...........enter Chaos Brigade led by the White Dragon Albion Vali Lucifer (don't get me started on the devil nonsense and family torn apart stuff), sworn rival to Issei and Ddraig, they are trying to upset that balance and also to bring Great Red the Dimensional Dragon (DD.....see it's the dragon not the cup size) forth doing it. The 3rd season introduces Loki as a member of the Chaos Brigade along with Koneko's sister and Son Goku (actual mythology not DBZ), with Loki entering the fray that's when Odin and the rest of the Norse mythology comes in.
The plot itself is surprisingly comprehensive, complex, yet once you watch it easy to understand. But it is DEFINITELY an ecchi anime, Issei essentially has a harem of girls: Rias, Akeno, Koneko, Xenovia, Asia and they all love him......it's very graphic in nature and heavily sexual, yet, even though it is like that and even though it isn't what you'd expect from this type of plot. The ecchi aspect never takes away from the story, in fact, Issei is a huge pervert like I mentioned and he uses being around the girls as motivation to train his and Ddraig's skills much to Ddraig's dismay being a great mythical creature. The girls constantly discourage his behaviour yet are at the same time all fond of him in their own unique way so they tolerate his nonsense. Rias, never saying it, is in love with him. Akeno treasures him as the first person to accept her for being half demon & half fallen angel. Koneko hated him at first yet once he helped deal with her inability to accept her catgod powers she grew fond of him. Asia loves how kind he is. Xenovia is naive as heck and just wants to have sex for procreation purposes. They tolerate his nonsense but all care, as does he, he cares about them all despite the way he sometimes acts and he too is obviously in love with Rias.
It may sound just absolutely awful and it may not be everyone's cup of tea but it proves that an ecchi can contain a really good plot without being ruined by the heavy sexual tones. Or at least the heavy sexual tones that come with an ecchi anime didn't ruin it for me. Some people may not enjoy it but to each their own. I'm looking forward to the 4th season.
Here's a few action pictures (no if you want the other action pictures look those up or watch the show)
Enjoy what you enjoy and keep watching what you're watching but never be afraid to try something new if someone suggests it, that's how I found out about Monster Musume for instance, but yes be open to all types of shows and don't limit yourself.