Can't tell if Reisen is being perverted or genuinely being concerned about her Master's chest.
And if Eirin is taking it as a weird way to say she's getting old or she just really likes those clothes and doesn't want to let them go anytime soon.
...I actually don't think it's reisen. Those are some very mannish arms, and the way Eirin is gripping her right hand seems like a veiled threat to the balls.
Not to mention, it's not in line with how Reisen otherwise acts in noizu's work.