You arrive at the park soon after, where several groups of onlookers have assembled to look at the damage for themselves. Your investigation will have to be subtle, so you message Lala and ask her to come in some casual clothes so as to avoid attracting attention. The order is then relayed to both of her sisters – who have somehow agreed to come along and give you a hand with this problem. Lala is quick to leap into your arms and plant her lips on yours as she steps through the breach.
"Thank you for summoning me again, hubby!"
Lala is exuberant as always, bouncing around the area with her usual sense of energy. She's going to be the one easing her sisters into this new situation. Thankfully, they come from a world that's very similar to yours; just without the aliens and genetically modified assassins. As for the park, it's plain to see that something strange is going on. It wasn't the biggest or densest green space around – but the entire thing has withered away. All of the greenery has turned a muddy brown and died off. You feel a little sad that something like this is being done to your city.
"Momo isn't going to be happy about this," Lala states soberly, having taken a second to observe the damage.
"We're going to want her help if we're finding out who did it."
"It's almost enough to make her forget about the harem plan…"
"She's still working on that?"
Lala smiles, "That's right! I've been updating her on your progress – and she's composing a sophisticated 'harem hierarchy' to make sure that everyone gets along and is on equal footing."
You get the distinct impression that Lala has bragged about you so much that Momo doesn't really know what you're like for real. She must think you're some kind of insane lust monster. Aside from that one time, it's not the case, and that was an exception because Lala decided to feed you an experimental drug.
"I guess we'd better summon them and explain what's going on."
You insert their cards into the Sledgehammer and pull the trigger with some trepidation. Lala is going to be a prickly customer just like Koneko. Hopefully her immediate aversion to you won't preclude getting her help on stopping whatever plan the aliens have come up with. The fabric of reality is shattered into pieces, and soon enough both pink-haired aliens appear before you with a sense of wonderment on their faces. Now that you get to see them in person, their resemblance to Lala is very much evident.
As for the rest of their physical attributes, it's impossible to not acknowledge that Nana clearly got the short end of the stick on that front. Lala is the tallest and curviest, Momo is in the middle, and Nana is rocking what can most politely be described as a very 'thin' body type. One of her defining personality traits is her hatred of people implying that she has a flat chest. Even though in this case it's true.
Momo's look of amazement turns into one of smugness, "I see. So, sis finally decided to introduce you to us! Nice to meet you, I'm Momo."
"W-Wait a second – why are you just going along with this? He just summoned us from another universe! I thought Lala was making it up!" Nana cries.
"It's very nice to meet both of you, finally."
Momo shakes your hand, but Nana is still shell-shocked from being brought to another world. Did she think that Lala was running away and hiding somewhere during your adventures together? Lala wraps her arms around their shoulders and pulls them in for a three-way hug. "I'm so happy that you all get to meet him!"
Nana huffs and turns away; "He's nothing special. You made him sound really impressive!"
Momo giggles; "Being willing to marry three sisters and heirs to a space empire is impressive in its own way, don't you agree?"
Nana does not, "That just means he's a world class pervert! Why can't you be happy with Lala, you jerk?" Her tail waves angrily in the air behind her.
"Hm? But isn't having multiple spouses normal where you're from?" you ask. Lala has attested to such before.
"Not on Earth it isn't," Momo explains, "For the stability of the empire, our father desires for one person to unify the family. Since Lala already decided that you were the one and only man for her – we decided to come and see if you lived up to that reputation."
Nana continues to throw a fit; "I don't remember him looking like this in the show!"
"That's because you only watched the later arcs with me!" Lala argues back, "He doesn't have all of his powers and abilities just yet!" There's no guarantee that you will end up looking like the fictionalised you from their universe – but diving into the weeds of this argument is not a constructive use of your time. Nana is just being tsundere, as she is liable to do given her role in the manga.
Momo pokes her in the side, "If you aren't interested, I'll be happy to take your spot – Nana."
Nana stomps her foot, "H-Hey! Hands off my spot! I'm going to show you how a real wife does things!" Momo is a master of manipulating Nana into suddenly reversing her position on things. A little appeal to her competitive spirit and she is essentially proposing to you on the spot. Her face turns bright red as she realises what she just said. "N-Not that I'd want to marry someone like you! Don't think you're going to win me over that easily, pervert!"
She's a much more energetic tsundere than Koneko is.
"Listen, we can untangle the whole marriage thing later. I wanted to get your opinion on something that's happening here."
Momo turns to the exterminated plants with an angry scowl, "Wha- Who did this?! I'll beat them up!"
Nana crosses her arms, "Here she goes again."
"You'd be angry if you saw a bunch of injured animals! People who don't respect nature and its beauty really make me mad!"
You usher them towards one of the few areas that survived the attack; "I was hoping you could help us with that, since you can speak with plants and all."
Momo decides to rain on your parade with a dose of reality, "They don't have eyes, you know. They'll only be able to tell me what they experienced at the time." You come to a stop at the base of the tree and rub your brow in frustration. Did you just summon her for no good reason then? Regardless of whether the information will be useful – Momo still does the task at hand and kneels down next to one of the small trees that survive. She whispers to it out of earshot and listens intently for a moment.
"Poor thing – it says that the pollution started to spread two days ago during the evening."
Surprisingly precise for a being with no eyes or ears, "During the evening? I'll ask Mitsuru to try and get her hands on some security camera footage from that time frame. She might be able to spot the person responsible."
Nana has seemingly learned her lesson as she kneels down next to her sister: "I suppose if the plants die, then the animals will suffer too."
"That's right!" Lala nods, "So let's all work together and track down the one responsible!"
"But I'm not doing anything weird!" Nana qualifies, "If you think that I'm going to do anything lewd or hold hands, you have another thing coming!"
Momo's concern gives way to her usual smirk as a malicious idea comes to her head; "Lala, did you already sleep with your fiancé?"
Lala sees nothing wrong with answering the question honestly; "That's right! A good partner should always be ready to please and relieve sexual energy!" Nana's face turns bright crimson as she casually extols how fun having sex with you is. "He's really good at it. Last week we got together with Rias and…"
"Why are you talking about this so openly, you damn pervert?!" Nana cries, slapping her hand over Lala's mouth to prevent her from speaking any further on the topic.
Momo pouts and pushes the tips of her fingers together sheepishly, "I just wanted to know if our future husband is good enough for us. After all, he is going to be Emperor of the Universe and have hundreds and hundreds of spouses."
"Papa isn't going to approve of this guy!" Nana yells, "Not unless he can defeat him in battle!"
"We don't have to worry about that for now," Lala says.
Momo concurs with her elder sister, "That's right. He won't be able to travel through dimensions and show up here. That means we can take all the time we need getting to know him, thoroughly." She sticks her tongue out as Nana continues to blister with incandescent rage. These two are about to come to blows over this. You take a moment to send your discovery to Mitsuru, who responds with a thumbs up emoji.
When you come back to the trio of alien sisters – they're in the middle of another entirely different argument to the one you left them on. Lala is visibly cross with Nana, "I'm an adult. I can choose to do whatever I please with my fiancé."
"Papa's going to kill you if he finds out!"
"But he won't! Not unless you tell him!"
Momo has a guilty look on her face now that things have turned into a war of words. Lala is a kind soul, so seeing her get into an actual argument with someone comes as a shock. It's a whole new side of the usually peppy girl. You approach the trio and hold your hands up to try and cool things off before they start shooting lasers at each other.
"Let's just worry about finding the culprit first, please? I didn't mean to make all of you fight over this."
"It's not your fault," Lala sighs, "I just think that Nana should stop being so stubborn. She's an even bigger fan of you than I am."
Nana's face screams betrayal, "Am not!"
"Yes, you are!" Momo responds, "Your entire room is filled with merchandise from the series. You have every toy, poster, manga volume, mega disc release, you even bought some of the props from the live action drama adaptation. And you think that fanfiction folder is a secret – but it's not!"
Nana chews on her bottom lip, "Grrr."
When you decided to summon the siblings for a meeting, you didn't anticipate that it would turn into a petty sibling argument over whether Nana actually likes you or not. Momo and Lala are all-in on the harem train, but Nana is still rocking that tsundere persona come what may. You clap your hands together again and decide to try again. "Stop arguing with each other. If Nana doesn't want to do anything, I'm going to respect her decision."
This time it works. Nana gives you a mute nod affirming that she agrees with your perspective. Momo and Lala are just too impatient to get her involved in the harem. Everyone has to go through a period of adjustment, even if they come from worlds where polygamy isn't considered a social taboo. You have to imagine that such relationships are still rare, requiring multiple consenting parties to go through with it. People start fights over the tiniest things sometimes, expecting harems to be normal is a step too far.
Your phone vibrates.
Mitsuru is to the point, "I checked the area at the time you specified. It's no surprise, but that imbecile is there with one of his androids again. They seem to be using it to inject the plant killing compound into the ground. A few hours later and the entire area was starting to die out."
"Great, so it's fast acting too."
"The worst-case scenario is that it lingers in the soil for a prolonged period of time and renders it infertile, or that residue runs off into a local water supply and accumulates in the animals and people that drink from it. Getting a pure sample of the compound they use would be a big help in taking counter-action. I presume you'll be capable of retrieving one from them?"
"Sure – if we can find out where they're hiding."
"I wouldn't worry about that. I'm taking proactive measures to watch over green areas in and around the city. If anything suspicious shows up, I'll know about it." You really hope that she isn't just sitting at her computer watching security feeds. Mitsuru hangs up and leaves you to navigate the fine line between pissing Nana off and winning her over.
"Since we're all here, how about we go for something to eat?" Lala suggests.
"That sounds nice," Momo agrees.
Nana is less excited, "Sure, I guess…"
You pull up a map on your phone and search for nearby eateries, "I might know a few good places."