Onegai☆Twins

Crossover in both appear Mizuho-sensei and other characters 

this anime has same style) probably it willl be crossover) it looks like ichika is a daughter of mizuho from onegai teacher? bsides alien look alike) 

Two (almost) sisters of the same age competing for the love of their brother. Kiss x Sis has more ecchi situations... 

I strongly urge fans of Onegai Twins to watch Koi Kaze. Both shows deal with the topic of incest, specifically a romantic love between brother and sister, but Koi Kaze actually brings up legitimate issues that could arise if siblings decided to become a couple. There's no peer approval, no understanding family members, no marriage, no 'love-finds-a-way', only a strong rejection from society. Additionally, Koi Kaze analyzes realistically the psychological profile of a brother that falls in love with their sister (and vice-versa) without sugar-coating it; the heavy mental pitfalls that befall the pair - a mixture of self-loathing and never-ending anxiety - are a hard, but refreshing, watch. If you want to see the incest taboo explored to its full depth with masterful, mature lens, watch Koi Kaze. read more 

Both series feature a guy trying to figure out who his sister is. 

If you liked Onegai Twins I recommend watching this next. It's alot like Onegai Twins due to two sisters trying to be with their brother. (not in the weird incest way that some think >.<)  

in both anime the main character falls in love with two girls who are related to him in domest na kanojo i falls in love with with his two step sister where both sister are related to each other in blood where in Onegai☆Twins the main character falles in love with two girld who clames to be his long lost twin sister the only twist is that only one of them is his twin sister and he have to find out which of them is his sister and which of them is not so he could accept their feelings properly  

Forbidden love is one of those genres in the anime world that's explored in both series. In both series, there is a forbidden romance between the main characters. Although Onegai Twins focuses more on a love triangle, both series contains rivals and drama. Both series also has comedy although Boku wa Imouto ni Koi wo Suru focuses more on the drama side. Additionally, both anime(s) have that mature and emotional side where the main character struggles to find his way throughout the story. 

Incestuous feelings. Need I say more? Both shows have a male protagonist that has complicated feelings towards his both sister and another girl, so a love triangle ensues. Both shows are very visually beautiful, emotional and feature memorable soundtracks. 

Don't get Twins confused with Teacher. both are completely different. Both Twins and M;Y involve a guy who has recently returned to his hometown after an extremely long time, and begins to find friends that he forgot he had. One of the females always has a crush on him, and the others support her even though the guy shows no interest in them. This is an anime of hardship. 

both animes are similar because its is basically about secret love. They will both have you crying laughing and wishing those lucky characters were you ^_^ 

this 2 anime is so a like to etch other, girls fall in love with the guy but may be his sister. But both guys are really diferent from etch other! 

they both have the theme that one of the familiy member will fall in love with the other... 

twins twins twins