Hah! Just increase Irish age to 9 or 10 when he was in the camp, that would make more sense. Since the reader haven't knew his backstory, unlike us.
Side note - Yes, since To-love-Ru has more Harem antic than I.S., I had to add even more wham and plot in the corssover.
Small sample of interaction
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Ren: "My name is Ren Elsie Jewelria, Australian I.S. Cadet Representative, I hope we can get along"
Class B: *Silent*
Lingyin: "Are you sure you're not a crossdresser"
Ren: "What the... you"
Lingyin: "Look, his voice isn't that deep, and look at that girly face... you remind me of that green-haired Pop singer"
Ren: "You... %#*@%!^*!"
Lingyin: "WHAT?! I'm not a %#*@%!^*!! You want a fight?! Fine!"
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Being called girly is Ren's berserk button, and they'll have a lot of foe yay.