Is this counted as rape since Danbooru defines "rape" as "Forcing perverted or sexual acts on an unwilling participant", and Zuikaku forced herself on Shoukaku even though Shoukaku didn't want to and told her to stop when she didn't wear a condom?
In real life, that may qualify as rape. If the guy continues sex but without a condom without her consent, I would call that rape. However, when it comes to doujinshi and the like, the lines between consent and nonconsent isn't quite clear. After all, there are many instances in manga where a girl will say "stop!" or "please don't!" even if she clearly wants it. It's simply there for viewer's pleasure and Japanese women tend to do this in real life as well. Concerning Danbooru's definition of rape, I've seen plenty of images similar to this situation and most don't qualify as legitimate rape. Rather, the girl is just annoyed that s/he ejaculated into her even though she told him/her not to, but it's not like she's yelling at him/her and calling him/her a rapist. So regarding this picture, I wouldn't count it as rape. After Zuikaku is done with her, it looks like Shoukaku is more concerned with getting pregnant than the fact Zuikaku came inside without consent (although it is true Shoukaku is worried about getting pregnant BECAUSE she came inside). At any rate, I don't see Shoukaku reporting Zuikaku to the police for rape.
This work has been deleted from Pixiv, so let's try to preserve this.
Ah...*Tremble...*Ah~*Spurt*ZuikakuHaaSo... good...Ah*Squish*Ngh*Squetch*AhNo, don't...The sense of touch...AhNgh...Hm...HaaHm... Urk...HaaZu, Zuikaku?Are you listening!? You can't!Shoukaku-neeI'm comingHaaZuika...Shoukaku-nee...Take it out... Hey Zuikaku!HaaHmEe...Haa...Hey Zuikaku!*Tremble...**Dribble*Wait, you forgot the condom...HmAh hm*oof**Bow bow*Zuikaku...HaaHaa...*Twitch*I'm coming...Wha-, no-, no don'tI'm sorry...HaaDon't Zuikaku, I'll get pregnant!*Squetch**Spurt**Steam*Haa*Twitch*Shoukaku-neeDon't come inside, okay? Pull out, got it?Haa*Twitch*Shoukaku-nee....I'll get pregnant-Haa*Twitch*Yo-, you can't Zuikaku... You have to put on a condomI told you... not to...HaaHaaShoukaku-neeShoukaku-neeHm*Squish**Spurt**Spurt*I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorry, I'm sorryHaaHaa haa*twitch*Haa...Zuikaku?HaaHaaAhHaaHaa*Tremble**Twitch**Spurt*HaaHaaPfaa*dizzy*But don't worry... I'll take full responsibility!*Squeeze...*I will definitely make Shoukaku-nee happy!If I really get pregnant, what am I going to do...?No!!You big dummy!Zuikaku, I don't even know anymore!END!!And I told you over and over again you couldn't*Hmph*That's not the thing to say right now!