Edit in JSFiddle

$(function () {
    var baloonFunction = function() {
        var x = 4;    // May
        var y = this.yAxis[0].series[0].data[x].y;
        $('#text').css({top: this.yAxis[0].toPixels(y), left: this.xAxis[0].toPixels(x)});
    };
    $('#container').highcharts({
        chart: {
            type: 'line',
            marginRight: 130,
            marginBottom: 25,
            events: {
                load: baloonFunction,
                redraw: baloonFunction 
            }
        },
        title: {
            text: 'Monthly Average Temperature',
            x: -20 //center
        },
        subtitle: {
            text: 'Source: WorldClimate.com',
            x: -20
        },
        xAxis: {
            categories: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
                         'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
        },
        yAxis: {
            title: {
                text: 'Temperature (°C)'
            },
            plotLines: [{
                value: 0,
                width: 1,
                color: '#808080'
            }]
        },
        tooltip: {
            valueSuffix: '°C'
        },
        legend: {
            layout: 'vertical',
            align: 'right',
            verticalAlign: 'top',
            x: -10,
            y: 100,
            borderWidth: 0
        },
        series: [{
            name: 'Tokyo',
            data: [7.0, 6.9, 9.5, 14.5, 0, 21.5, 25.2, 26.5, 23.3, 18.3, 13.9, 9.6]
        }, {
            name: 'New York',
            data: [-0.2, 0.8, 5.7, 11.3, 17.0, 22.0, 24.8, 24.1, 20.1, 14.1, 8.6, 2.5]
        }, {
            name: 'Berlin',
            data: [-0.9, 0.6, 3.5, 8.4, 13.5, 17.0, 18.6, 17.9, 14.3, 9.0, 3.9, 1.0]
        }, {
            name: 'London',
            data: [3.9, 4.2, 5.7, 8.5, 11.9, 15.2, 17.0, 16.6, 14.2, 10.3, 6.6, 4.8]
        }]
    });
});

<script src="http://code.highcharts.com/highcharts.js"></script>
<script src="http://code.highcharts.com/modules/exporting.js"></script>

<div id="chart_area">
<div id="container" style="min-width: 400px; height: 400px; margin: 0 auto"></div>
<div id="text">
    <pre>＿人人 人人＿
＞ 突然の死 ＜
￣Y^Y^Y^Y￣</pre>
</div>
</div>

#chart_area{
    position: relative;
}
#text {
    position: absolute;
    top: 0;
    left: 0;
    width: 200px;
    text-align: center;
    margin-left:-100px;
}
#text pre {
    margin: 0;
}